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OpenGL 2d with direct3d: how to display argb data in a window

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Hey, I have a rectangle (a piece of memory) that I fill with argb data. I would like to display it in a window, using direct3d. I have 3 questions about that. 1) I've read several tutorials. One solution would be to use the sprite interface. Then create a texture, fill it with data and render it onto the surface. I have written that code:
// the variable d contains a window and d3d object, device and sprite



  d->device->Clear (0, NULL,
                    D3DCLEAR_TARGET | D3DCLEAR_ZBUFFER,
                    D3DCOLOR_ARGB (0, 0, 0, 0),
                    1.0f, 0);

  d->device->BeginScene ();

 // Here is my argb surface, named 'surf'

  w = 64;
  h = 64;
  depth = 4;
  pitch = depth * w;
  surf = malloc (depth * w * h);
  if (!surf) return 0;
  ZeroMemory (surf, depth * w * h);

  tmp = (unsigned char *)surf;
  for (r = 0; r < w; r++) {
    for (g = 0; g < h; g++, tmp += depth) {
      tmp[0] = (r * 2 + foo) % 256;
      tmp[1] = (g + foo) % 256;
      tmp[2] = (w - 1 - g) * 4;
    }
  }
  foo++;

  rect.left = 0;
  rect.top = 0;
  rect.right = w;
  rect.bottom = h;

  // FIXME : other flags might speed up things
  d->sprite->Begin (0);

  d->device->CreateTexture (w, h, 0, 0,
                            D3DFMT_A8R8G8B8,
                            D3DPOOL_DEFAULT,
                            &texture, NULL);

  // I have to fill the texture with the data of surf

  d->sprite->SetTransform (&matrix);
  d->sprite->Draw (texture, &rect, NULL, NULL, D3DCOLOR_ARGB (0, 0, 0, 0));
  d->sprite->End ();

  d->device->EndScene ();
  d->device->Present (NULL, NULL, NULL, NULL);


As I mentioned in a comment of that code, I have to fill the texture with the surf data. I've looked at a lot of tutorials, sites, etc... I didn't find any code to do that. I find code to fill a texture from a file, but not from a piece of memory. So my first question is: is it possible, and if yes, how ? 2) My second question is about speed. My main cincern is speed. I've already written a code with directdraw 7. The speed is the same than a similar code on linux, using software routines. I don't know if it is normal or not. I wanted to get more speed, so I tried to do that with direct3d, in order to use hardware accelerated features of d3d. With all the doc and tutorial I've read, I found several things to speed up all that stuff: a) Using vertices instead of sprites b) Using the immediate mode of d3d (see http://msdn.microsoft.com/archive/default.asp?url=/archive/en-us/dnardir3d/html/d3dim.asp) Is it correct ? and if so, do you have some documentation about vertices or immediate mode, in order to achieve what I want ? Also, if there are better solutions (that is, faster techniques related to d3d to do what I want), I would be pleased to know them 3) Finally, between opengl and d3d, is there a difference in speed ? (for what I want to do) thank you very much Vincent Torri [Edited by - Vincent Torri on July 11, 2007 3:06:58 PM]

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Quote:
Original post by Vincent Torri
So my first question is: is it possible, and if yes, how ?
Yes, it's certainly possible.
You'll want to lock the top level of the texture (and each level in turn if you have mipmaps - which you almost certainly don't want - see #2), that'll give you a pointer to memory you can copy into.

EDIT: Here's some code from my engine:

void PTexture::Update(const u32* pData)
{
Assert(m_desc.Usage & D3DUSAGE_DYNAMIC, "Update() only valid on dynamic textures");
Assert(m_nLevels == 1, "Can only Update() textures with one mip level in them");

// Lock texture
D3DLOCKED_RECT d3dRect;
HRESULT hResult = m_pTexture->LockRect(0, &d3dRect, NULL, 0);
if(FAILED(hResult))
{
ELog::Get().DebugFormat(L"TEXTURE : IDirect3DTexture9::LockRect() failed. Error: %s\n",
DXGetErrorString(hResult));
return;
}

// Fill - do a fast copy if we can
if((u32)d3dRect.Pitch == m_desc.Width * 4)
{
memcpy(d3dRect.pBits, pData, m_desc.Width * m_desc.Height * 4);
}
else
{
// Need to copy scanline by scanline to avoid crapping up the pitch
for(UINT y=0; y<m_desc.Height; ++y)
{
memcpy((BYTE*)d3dRect.pBits + y*d3dRect.Pitch, pData, m_desc.Width * 4);
pData += m_desc.Width;
}
}

// Unlock
m_pTexture->UnlockRect(0);
}



Quote:
Original post by Vincent Torri
2) My second question is about speed. My main cincern is speed. I've already written a code with directdraw 7. The speed is the same than a similar code on linux, using software routines. I don't know if it is normal or not. I wanted to get more speed, so I tried to do that with direct3d, in order to use hardware accelerated features of d3d.

With all the doc and tutorial I've read, I found several things to speed up all that stuff:

a) Using vertices instead of sprites
b) Using the immediate mode of d3d
Notice the date on that link: 1997; 10 years ago [smile] - non-immediate mode hasn't existed since D3D5 or so; All D3D is immediate mode now, and there's no retained mode.
Using vertices instead of sprites won't make much difference at all here.

Things that will make a difference though:
  • Create your texture as D3DUSAGE_DYNAMIC. Otherwise the texture will probably be dumped into video RAM and updating it will be extremely expensive.
  • Don't create any mip-maps (Set the 3rd parameter of CreateTexture() to 1 instead of 0)
  • Don't update the texture every frame if you can help it (depends what you're doing really). It's better to update the texture once at load time, and then never have to touch it. If that's the case, don't bother with D3DUSAGE_DYNAMIC.
  • If you update and render the texture every frame, it might be a good idea to use 4 or so textures in a round-robbin fassion. That way D3D doesn't have to wait for the data to be uploaded to the graphics card before it renders the frame, but you'll get 4 frames of "lag" on the texture.
  • When you lock the texture, you can write directly into that, instead of writing to a memory buffer, then copying that buffer to the locked texture.

    If you're using dynamic textures, then you can lock the texture, if not, you'll have to either put the texture into D3DPOOL_MANAGED, or use IDirect3DDevice9::UpdateTexture to copy the data to the texture instead.

    Quote:
    Original post by Vincent Torri
    3) Finally, between opengl and d3d, is there a difference in speed ? (for what I want to do)
    Almost certainly not. I can't really day for sure, since I'm not an OpenGL person, but I'll be surprised if there's a significant performance difference provided both ways are optimal for their own API.

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    Quote:
    Original post by Evil Steve
    You'll want to lock the top level of the texture (and each level in turn if you have mipmaps - which you almost certainly don't want - see #2), that'll give you a pointer to memory you can copy into.

    haa, ok. thank you ! I'll try that.
    Quote:

    Quote:
    Original post by Vincent Torri
    2) My second question is about speed. With all the doc and tutorial I've read, I found several things to speed up all that stuff:

    a) Using vertices instead of sprites
    b) Using the immediate mode of d3d

    Notice the date on that link: 1997; 10 years ago - non-immediate mode hasn't existed since D3D5 or so; All D3D is immediate mode now, and there's no retained mode.
    Using vertices instead of sprites won't make much difference at all here.

    ok. That saves me some work. That immediate mode is a bit a pain to implement. Same for vertices, btw.
    Quote:

    Things that will make a difference though:
  • Create your texture as D3DUSAGE_DYNAMIC. Otherwise the texture will probably be dumped into video RAM and updating it will be extremely expensive.
  • Don't create any mip-maps (Set the 3rd parameter of CreateTexture() to 1 instead of 0)
  • Don't update the texture every frame if you can help it (depends what you're doing really). It's better to update the texture once at load time, and then never have to touch it. If that's the case, don't bother with D3DUSAGE_DYNAMIC.
  • If you update and render the texture every frame, it might be a good idea to use 4 or so textures in a round-robbin fassion. That way D3D doesn't have to wait for the data to be uploaded to the graphics card before it renders the frame, but you'll get 4 frames of "lag" on the texture.
  • When you lock the texture, you can write directly into that, instead of writing to a memory buffer, then copying that buffer to the locked texture.

    If you're using dynamic textures, then you can lock the texture, if not, you'll have to either put the texture into D3DPOOL_MANAGED, or use IDirect3DDevice9::UpdateTexture to copy the data to the texture instead.

  • What I want to do is the engine of a canvas library. What it does is exactly what I try to do : having a rectangle of some size (i know that size only at runtime, so I think that I have to create the texture each time I need it) with some data, and drawing it at some position. These rectangles are created by the user of the lib.

    But the engine is written such that I have to render a sequence of such rectangles. I know the number of these rectangles and their size. So I think that I can do what you describe in your 4th point ("round-robin fashion"). Could you please elaborate a bit on that technic, please ? Or maybe is there something else to do in that case ?
    Quote:

    Quote:
    Original post by Vincent Torri
    3) Finally, between opengl and d3d, is there a difference in speed ? (for what I want to do)
    Almost certainly not. I can't really day for sure, since I'm not an OpenGL person, but I'll be surprised if there's a significant performance difference provided both ways are optimal for their own API.

    ok.

    thank you very much for your answer !

    Vincent Torri

    PS: if you are interested, that canvas is named 'evas' and is part of the enlightenment project.

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    Quote:
    Original post by Vincent Torri
    What I want to do is the engine of a canvas library. What it does is exactly what I try to do : having a rectangle of some size (i know that size only at runtime, so I think that I have to create the texture each time I need it) with some data, and drawing it at some position. These rectangles are created by the user of the lib.
    You definitely want to avoid creating the texture every frame. Only create the texture when the canvas size changes, otherwise you'll get horrible performance (Creating D3D resources is very expensive). Locking the texture each frame (Or using the 4-texture method) is ok though, so long as you create the texture as dynamic.
    I'm not sure exactly how often you have to lock the texture to make a dynamic texture better, but if you're doing it more than once a second, I'd go for dynamic, and even if you lock it less frequently, you're likely to see a stutter with a non-dynamic texture (See the 4-texture method stuff below) while D3D uploads the texture.

    Quote:
    Original post by Vincent Torri
    But the engine is written such that I have to render a sequence of such rectangles. I know the number of these rectangles and their size. So I think that I can do what you describe in your 4th point ("round-robin fashion"). Could you please elaborate a bit on that technic, please ? Or maybe is there something else to do in that case ?
    If you have one texture, it goes like this:
    Lock texture and fill it with data
    Render textured quad / sprite
    However, in the background, this is happening:
    Lock texture and fill it with data
    Unlock texture. D3D now starts to send the texture to the video card
    Request rendering of textured quad / sprite
    D3D has to wait for the texture to finish transferring to video memory before it can render the textured quad
    Transfer completes, quad gets rendered

    Now, you can use several textures (I'll only use 2 in this example) to get around the stall while D3D uploads the texture. Your code does this:
    Startup: Lock and fill all textures
    Start of frame 1:
    Lock texture B and fill it with data
    Render textured quad / sprite with texture A
    Present. End of frame 1
    Start of frame 2:
    Lock texture A and fill it with data
    Render textured quad / sprite with texture B
    Present. End of frame 2
    Start of frame 3:
    Lock texture B and fill it with data
    Render textured quad / sprite with texture A
    Present. End of frame 3
    So, you're constantly going through the textures, one after another (If you had 4 textures, then frame 1 you'd update D and use A, frame 2 you'd update A and use B, frame 3 you'd update B and use C, frame 4 you'd update C and use D, repeat).
    The point is that there's now a 1 frame gap between locking a texture and it being used. That means you have 1 frame of "lag", since you're displaying the texture from the previous frame, but it gives D3D a whole extra frame to upload the texture to the card.

    If the bottleneck in your application does turn out to be texture uploading, this is a nice and easy fix for it. But I'd profile your app (PIX, in the DirectX SDK is good for this, and NVPerfHUD for NVidia cards) and see if this is actually a bottleneck, since it's possible that D3D has enough time to transfer the texture to the graphics card anyway, and adding this round-robbin system will only introduce lag in your texture, and require more video memory.


    Incidently, using a dynamic texture usually causes D3D (The video card driver, more correctly) to put the texture into AGP memory, or somewhere else where it's faster for D3D to access but slower for the card, so it averages out better. Not using a dynamic texture usually places the texture into video memory, and getting a texture there from CPU-accessible memory can be pretty expensive.

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    ok, I understand a bit more how it works, now. Creating the texture before is a bit how I managed to do the same thing with directdraw and its surfaces.

    about the dynamic texture, I can't know if there will be animations or not. So I'll use dynamic textures. The best is checking if an animation is done or not, and use a dynamic texture in that case. I'll do some tests.

    I'll check if I can use the "round-robin" technic in my engine. It can be very interesting for animations.

    thank you for your explanations.

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    Evil Steve:

    About your code:

    [source lang=cpp]
    for(UINT y=0; y<m_desc.Height; ++y)
    {
    memcpy((BYTE*)d3dRect.pBits + y*d3dRect.Pitch, pData, m_desc.Width * 4);
    pData += m_desc.Width;
    }



    maybe you should avoid y*d3dRect.Pitch and use pointer arithmetic, maybe you can also compute m_desc.Width * 4 as a pitch and use it.

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    Quote:
    Original post by Vincent Torri
    Evil Steve:

    About your code:

    *** Source Snippet Removed ***

    maybe you should avoid y*d3dRect.Pitch and use pointer arithmetic, maybe you can also compute m_desc.Width * 4 as a pitch and use it.


    Surface width * bytes per pixel may not be equal to the pitch. If you assume that it is, you'll run into problems later.

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    as I'm away from my home computer and as i didn't take with me my small test code, I wanted to re-write it.

    Unfortunately, it does not work. Here is the complete code:


    // g++ -g -Wall -o d3d d3d.cpp -ld3d9 -ld3dx9d

    #include <cstdlib>
    #include <cstdio>

    #include <windows.h>
    #include <d3d9.h>
    #include <d3dx9.h>

    typedef struct Data Data;

    struct Data
    {
    LPDIRECT3D9 object;
    LPDIRECT3DDEVICE9 device;
    LPD3DXSPRITE sprite;
    LPDIRECT3DTEXTURE9 texture;
    int mask_r;
    int mask_g;
    int mask_b;
    };


    static LRESULT CALLBACK
    MainWndProc(HWND hwnd,
    UINT uMsg,
    WPARAM wParam,
    LPARAM lParam)
    {
    switch (uMsg)
    {
    case WM_CREATE:
    return 0;
    case WM_DESTROY:
    PostQuitMessage(0);
    return 0;
    case WM_CLOSE:
    PostQuitMessage(0);
    return 0;
    default:
    return DefWindowProc(hwnd, uMsg, wParam, lParam);
    }
    }

    Data *
    data_init (HWND window,
    int width,
    int height)
    {
    D3DPRESENT_PARAMETERS pp;
    D3DDISPLAYMODE dm;
    D3DSURFACE_DESC sd;
    Data *d;

    d = (Data *)malloc (sizeof (Data));
    if (!d)
    goto no_data;

    d->object = Direct3DCreate9 (D3D_SDK_VERSION);
    if (!d->object)
    goto no_object;

    if (FAILED (d->object->GetAdapterDisplayMode (D3DADAPTER_DEFAULT, &dm)))
    goto no_device;

    ZeroMemory(&pp, sizeof(pp));
    pp.BackBufferFormat = dm.Format;
    pp.BackBufferCount = 1;
    pp.SwapEffect = D3DSWAPEFFECT_FLIP;
    pp.hDeviceWindow = window;
    pp.Windowed = TRUE;

    if (FAILED(d->object->CreateDevice (D3DADAPTER_DEFAULT,
    D3DDEVTYPE_HAL,
    window,
    D3DCREATE_HARDWARE_VERTEXPROCESSING,
    &pp,
    &d->device)))
    goto no_device;

    if (FAILED (D3DXCreateSprite (d->device, &d->sprite)))
    goto no_sprite;

    if (FAILED (d->device->CreateTexture (width, height, 1,
    D3DUSAGE_DYNAMIC,
    dm.Format,
    D3DPOOL_DEFAULT,
    &d->texture, NULL)))
    goto no_texture;

    if (FAILED (d->texture->GetLevelDesc (0, &sd)))
    goto no_level_desc;

    switch (sd.Format) {
    case D3DFMT_A8R8G8B8:
    case D3DFMT_X8R8G8B8:
    d->mask_r = 0x00ff0000;
    d->mask_g = 0x0000ff00;
    d->mask_b = 0x000000ff;
    break;
    case D3DFMT_R5G6B5:
    d->mask_r = 0xf800;
    d->mask_g = 0x07e0;
    d->mask_b = 0x001f;
    break;
    default:
    goto no_level_desc;
    }

    return d;

    no_level_desc:
    d->texture->Release ();
    no_texture:
    d->sprite->Release ();
    no_sprite:
    d->device->Release ();
    no_device:
    d->object->Release ();
    no_object:
    free (d);
    no_data:
    return NULL;
    }

    void
    data_shutdown (Data *d)
    {
    if (!d)
    return;

    d->texture->Release ();
    d->sprite->Release ();
    d->device->Release ();
    d->object->Release ();
    free (d);
    }

    void
    data_paint (Data *d)
    {
    D3DLOCKED_RECT d3d_rect;
    RECT rect;
    int w;
    int h;
    int depth;
    int pitch;
    unsigned char *tmp;
    unsigned char *d3d_tmp;
    static int foo = 0;

    void *surf;

    w = 64;
    h = 64;
    depth = 4;
    pitch = depth * w;

    surf = calloc (w * h * depth, 1);
    if (!surf) {
    printf ("pas bon \n");
    return;
    }
    tmp = (unsigned char *)surf;
    for (int r = 0; r < w; r++) {
    for (int g = 0; g < h; g++, tmp += depth) {
    tmp[0] = (r * 2 + foo) % 256;
    tmp[1] = (g + foo) % 256;
    tmp[2] = (w - 1 - g) * 4;
    }
    }
    foo++;

    rect.left = 0;
    rect.top = 0;
    rect.right = w;
    rect.bottom = h;

    if (FAILED (d->device->BeginScene ()))
    return;

    if (FAILED (d->sprite->Begin (0)))
    return;
    if (FAILED (d->texture->LockRect (0, &d3d_rect, NULL, D3DLOCK_DISCARD))) {
    d->sprite->End ();
    d->device->EndScene ();
    return;
    }

    tmp = (unsigned char *)surf;
    d3d_tmp = (unsigned char *)d3d_rect.pBits;
    for (int j = 0; j < h; j++, tmp += pitch, d3d_tmp += d3d_rect.Pitch)
    memcpy (d3d_tmp, tmp, pitch);

    d->texture->UnlockRect(0);

    d->sprite->Draw (d->texture, &rect, NULL, NULL,
    D3DCOLOR_ARGB (0, 0, 0, 0));
    d->sprite->End ();

    d->device->EndScene ();
    d->device->Present (NULL, NULL, NULL, NULL);

    free (surf);
    }

    int WINAPI
    WinMain(HINSTANCE hinstance,
    HINSTANCE hPrevInstance,
    LPSTR lpCmdLine,
    int nCmdShow)
    #if 0
    main ()
    #endif
    {
    WNDCLASS wc;
    RECT rect;
    MSG msg;
    HINSTANCE instance;
    HWND window;
    Data *d;
    int width;
    int height;

    instance = GetModuleHandle(0);
    if (!instance)
    goto no_instance;

    ZeroMemory(&wc, sizeof(wc));
    wc.lpfnWndProc = MainWndProc;
    wc.hInstance = instance;
    wc.hIcon = LoadIcon (NULL, IDI_APPLICATION);
    wc.hCursor = LoadCursor (NULL, IDC_ARROW);
    wc.hbrBackground = (HBRUSH)(1 + COLOR_BTNFACE);
    wc.lpszClassName = "Direct3D_test";

    if(!RegisterClass(&wc))
    goto no_window_class;

    width = 320;
    height = 200;

    rect.left = 0;
    rect.top = 0;
    rect.right = width;
    rect.bottom = height;
    AdjustWindowRect (&rect, WS_OVERLAPPEDWINDOW | WS_SIZEBOX, FALSE);

    window = CreateWindow("Direct3D_test",
    "Direct3D_test",
    WS_OVERLAPPEDWINDOW | WS_SIZEBOX,
    CW_USEDEFAULT, CW_USEDEFAULT,
    rect.right - rect.left, rect.bottom - rect.top,
    NULL, NULL, instance, NULL);
    if (!window)
    goto no_window;

    d = data_init (window, width, height);
    if (!d)
    goto no_data;

    ShowWindow(window, SW_SHOWDEFAULT);
    UpdateWindow(window);

    while (GetMessage (&msg, NULL, 0, 0))
    {
    TranslateMessage (&msg);
    DispatchMessage (&msg);
    data_paint (d);
    }

    data_shutdown (d);
    DestroyWindow (window);
    UnregisterClass ("Direct3D_test", instance);
    FreeLibrary (instance);

    return EXIT_SUCCESS;

    no_data:
    DestroyWindow (window);
    no_window:
    UnregisterClass ("Direct3D_test", instance);
    no_window_class:
    FreeLibrary (instance);
    no_instance:
    return EXIT_FAILURE;
    }





    this program creates a window and displays a small animation in a 64x64 pixels large square at the top-left of the window. The window is created, but no animation is displayed.

    I don't really know where the problem is (maybe in the initialisation of direct3d, in data_init).
    does someone see the problem ?

    thank you very much

    [Edited by - Vincent Torri on July 29, 2007 12:19:52 PM]

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        Introduction
        Graphics APIs have come a long way from small set of basic commands allowing limited control of configurable stages of early 3D accelerators to very low-level programming interfaces exposing almost every aspect of the underlying graphics hardware. Next-generation APIs, Direct3D12 by Microsoft and Vulkan by Khronos are relatively new and have only started getting widespread adoption and support from hardware vendors, while Direct3D11 and OpenGL are still considered industry standard. New APIs can provide substantial performance and functional improvements, but may not be supported by older hardware. An application targeting wide range of platforms needs to support Direct3D11 and OpenGL. New APIs will not give any advantage when used with old paradigms. It is totally possible to add Direct3D12 support to an existing renderer by implementing Direct3D11 interface through Direct3D12, but this will give zero benefits. Instead, new approaches and rendering architectures that leverage flexibility provided by the next-generation APIs are expected to be developed.
        There are at least four APIs (Direct3D11, Direct3D12, OpenGL/GLES, Vulkan, plus Apple's Metal for iOS and osX platforms) that a cross-platform 3D application may need to support. Writing separate code paths for all APIs is clearly not an option for any real-world application and the need for a cross-platform graphics abstraction layer is evident. The following is the list of requirements that I believe such layer needs to satisfy:
        Lightweight abstractions: the API should be as close to the underlying native APIs as possible to allow an application leverage all available low-level functionality. In many cases this requirement is difficult to achieve because specific features exposed by different APIs may vary considerably. Low performance overhead: the abstraction layer needs to be efficient from performance point of view. If it introduces considerable amount of overhead, there is no point in using it. Convenience: the API needs to be convenient to use. It needs to assist developers in achieving their goals not limiting their control of the graphics hardware. Multithreading: ability to efficiently parallelize work is in the core of Direct3D12 and Vulkan and one of the main selling points of the new APIs. Support for multithreading in a cross-platform layer is a must. Extensibility: no matter how well the API is designed, it still introduces some level of abstraction. In some cases the most efficient way to implement certain functionality is to directly use native API. The abstraction layer needs to provide seamless interoperability with the underlying native APIs to provide a way for the app to add features that may be missing. Diligent Engine is designed to solve these problems. Its main goal is to take advantages of the next-generation APIs such as Direct3D12 and Vulkan, but at the same time provide support for older platforms via Direct3D11, OpenGL and OpenGLES. Diligent Engine exposes common C++ front-end for all supported platforms and provides interoperability with underlying native APIs. It also supports integration with Unity and is designed to be used as graphics subsystem in a standalone game engine, Unity native plugin or any other 3D application. Full source code is available for download at GitHub and is free to use.
        Overview
        Diligent Engine API takes some features from Direct3D11 and Direct3D12 as well as introduces new concepts to hide certain platform-specific details and make the system easy to use. It contains the following main components:
        Render device (IRenderDevice  interface) is responsible for creating all other objects (textures, buffers, shaders, pipeline states, etc.).
        Device context (IDeviceContext interface) is the main interface for recording rendering commands. Similar to Direct3D11, there are immediate context and deferred contexts (which in Direct3D11 implementation map directly to the corresponding context types). Immediate context combines command queue and command list recording functionality. It records commands and submits the command list for execution when it contains sufficient number of commands. Deferred contexts are designed to only record command lists that can be submitted for execution through the immediate context.
        An alternative way to design the API would be to expose command queue and command lists directly. This approach however does not map well to Direct3D11 and OpenGL. Besides, some functionality (such as dynamic descriptor allocation) can be much more efficiently implemented when it is known that a command list is recorded by a certain deferred context from some thread.
        The approach taken in the engine does not limit scalability as the application is expected to create one deferred context per thread, and internally every deferred context records a command list in lock-free fashion. At the same time this approach maps well to older APIs.
        In current implementation, only one immediate context that uses default graphics command queue is created. To support multiple GPUs or multiple command queue types (compute, copy, etc.), it is natural to have one immediate contexts per queue. Cross-context synchronization utilities will be necessary.
        Swap Chain (ISwapChain interface). Swap chain interface represents a chain of back buffers and is responsible for showing the final rendered image on the screen.
        Render device, device contexts and swap chain are created during the engine initialization.
        Resources (ITexture and IBuffer interfaces). There are two types of resources - textures and buffers. There are many different texture types (2D textures, 3D textures, texture array, cubmepas, etc.) that can all be represented by ITexture interface.
        Resources Views (ITextureView and IBufferView interfaces). While textures and buffers are mere data containers, texture views and buffer views describe how the data should be interpreted. For instance, a 2D texture can be used as a render target for rendering commands or as a shader resource.
        Pipeline State (IPipelineState interface). GPU pipeline contains many configurable stages (depth-stencil, rasterizer and blend states, different shader stage, etc.). Direct3D11 uses coarse-grain objects to set all stage parameters at once (for instance, a rasterizer object encompasses all rasterizer attributes), while OpenGL contains myriad functions to fine-grain control every individual attribute of every stage. Both methods do not map very well to modern graphics hardware that combines all states into one monolithic state under the hood. Direct3D12 directly exposes pipeline state object in the API, and Diligent Engine uses the same approach.
        Shader Resource Binding (IShaderResourceBinding interface). Shaders are programs that run on the GPU. Shaders may access various resources (textures and buffers), and setting correspondence between shader variables and actual resources is called resource binding. Resource binding implementation varies considerably between different API. Diligent Engine introduces a new object called shader resource binding that encompasses all resources needed by all shaders in a certain pipeline state.
        API Basics
        Creating Resources
        Device resources are created by the render device. The two main resource types are buffers, which represent linear memory, and textures, which use memory layouts optimized for fast filtering. Graphics APIs usually have a native object that represents linear buffer. Diligent Engine uses IBuffer interface as an abstraction for a native buffer. To create a buffer, one needs to populate BufferDesc structure and call IRenderDevice::CreateBuffer() method as in the following example:
        BufferDesc BuffDesc; BufferDesc.Name = "Uniform buffer"; BuffDesc.BindFlags = BIND_UNIFORM_BUFFER; BuffDesc.Usage = USAGE_DYNAMIC; BuffDesc.uiSizeInBytes = sizeof(ShaderConstants); BuffDesc.CPUAccessFlags = CPU_ACCESS_WRITE; m_pDevice->CreateBuffer( BuffDesc, BufferData(), &m_pConstantBuffer ); While there is usually just one buffer object, different APIs use very different approaches to represent textures. For instance, in Direct3D11, there are ID3D11Texture1D, ID3D11Texture2D, and ID3D11Texture3D objects. In OpenGL, there is individual object for every texture dimension (1D, 2D, 3D, Cube), which may be a texture array, which may also be multisampled (i.e. GL_TEXTURE_2D_MULTISAMPLE_ARRAY). As a result there are nine different GL texture types that Diligent Engine may create under the hood. In Direct3D12, there is only one resource interface. Diligent Engine hides all these details in ITexture interface. There is only one  IRenderDevice::CreateTexture() method that is capable of creating all texture types. Dimension, format, array size and all other parameters are specified by the members of the TextureDesc structure:
        TextureDesc TexDesc; TexDesc.Name = "My texture 2D"; TexDesc.Type = TEXTURE_TYPE_2D; TexDesc.Width = 1024; TexDesc.Height = 1024; TexDesc.Format = TEX_FORMAT_RGBA8_UNORM; TexDesc.Usage = USAGE_DEFAULT; TexDesc.BindFlags = BIND_SHADER_RESOURCE | BIND_RENDER_TARGET | BIND_UNORDERED_ACCESS; TexDesc.Name = "Sample 2D Texture"; m_pRenderDevice->CreateTexture( TexDesc, TextureData(), &m_pTestTex ); If native API supports multithreaded resource creation, textures and buffers can be created by multiple threads simultaneously.
        Interoperability with native API provides access to the native buffer/texture objects and also allows creating Diligent Engine objects from native handles. It allows applications seamlessly integrate native API-specific code with Diligent Engine.
        Next-generation APIs allow fine level-control over how resources are allocated. Diligent Engine does not currently expose this functionality, but it can be added by implementing IResourceAllocator interface that encapsulates specifics of resource allocation and providing this interface to CreateBuffer() or CreateTexture() methods. If null is provided, default allocator should be used.
        Initializing the Pipeline State
        As it was mentioned earlier, Diligent Engine follows next-gen APIs to configure the graphics/compute pipeline. One big Pipelines State Object (PSO) encompasses all required states (all shader stages, input layout description, depth stencil, rasterizer and blend state descriptions etc.). This approach maps directly to Direct3D12/Vulkan, but is also beneficial for older APIs as it eliminates pipeline misconfiguration errors. With many individual calls tweaking various GPU pipeline settings it is very easy to forget to set one of the states or assume the stage is already properly configured when in fact it is not. Using pipeline state object helps avoid these problems as all stages are configured at once.
        Creating Shaders
        While in earlier APIs shaders were bound separately, in the next-generation APIs as well as in Diligent Engine shaders are part of the pipeline state object. The biggest challenge when authoring shaders is that Direct3D and OpenGL/Vulkan use different shader languages (while Apple uses yet another language in their Metal API). Maintaining two versions of every shader is not an option for real applications and Diligent Engine implements shader source code converter that allows shaders authored in HLSL to be translated to GLSL. To create a shader, one needs to populate ShaderCreationAttribs structure. SourceLanguage member of this structure tells the system which language the shader is authored in:
        SHADER_SOURCE_LANGUAGE_DEFAULT - The shader source language matches the underlying graphics API: HLSL for Direct3D11/Direct3D12 mode, and GLSL for OpenGL and OpenGLES modes. SHADER_SOURCE_LANGUAGE_HLSL - The shader source is in HLSL. For OpenGL and OpenGLES modes, the source code will be converted to GLSL. SHADER_SOURCE_LANGUAGE_GLSL - The shader source is in GLSL. There is currently no GLSL to HLSL converter, so this value should only be used for OpenGL and OpenGLES modes. There are two ways to provide the shader source code. The first way is to use Source member. The second way is to provide a file path in FilePath member. Since the engine is entirely decoupled from the platform and the host file system is platform-dependent, the structure exposes pShaderSourceStreamFactory member that is intended to provide the engine access to the file system. If FilePath is provided, shader source factory must also be provided. If the shader source contains any #include directives, the source stream factory will also be used to load these files. The engine provides default implementation for every supported platform that should be sufficient in most cases. Custom implementation can be provided when needed.
        When sampling a texture in a shader, the texture sampler was traditionally specified as separate object that was bound to the pipeline at run time or set as part of the texture object itself. However, in most cases it is known beforehand what kind of sampler will be used in the shader. Next-generation APIs expose new type of sampler called static sampler that can be initialized directly in the pipeline state. Diligent Engine exposes this functionality: when creating a shader, textures can be assigned static samplers. If static sampler is assigned, it will always be used instead of the one initialized in the texture shader resource view. To initialize static samplers, prepare an array of StaticSamplerDesc structures and initialize StaticSamplers and NumStaticSamplers members. Static samplers are more efficient and it is highly recommended to use them whenever possible. On older APIs, static samplers are emulated via generic sampler objects.
        The following is an example of shader initialization:
        ShaderCreationAttribs Attrs; Attrs.Desc.Name = "MyPixelShader"; Attrs.FilePath = "MyShaderFile.fx"; Attrs.SearchDirectories = "shaders;shaders\\inc;"; Attrs.EntryPoint = "MyPixelShader"; Attrs.Desc.ShaderType = SHADER_TYPE_PIXEL; Attrs.SourceLanguage = SHADER_SOURCE_LANGUAGE_HLSL; BasicShaderSourceStreamFactory BasicSSSFactory(Attrs.SearchDirectories); Attrs.pShaderSourceStreamFactory = &BasicSSSFactory; ShaderVariableDesc ShaderVars[] = {     {"g_StaticTexture", SHADER_VARIABLE_TYPE_STATIC},     {"g_MutableTexture", SHADER_VARIABLE_TYPE_MUTABLE},     {"g_DynamicTexture", SHADER_VARIABLE_TYPE_DYNAMIC} }; Attrs.Desc.VariableDesc = ShaderVars; Attrs.Desc.NumVariables = _countof(ShaderVars); Attrs.Desc.DefaultVariableType = SHADER_VARIABLE_TYPE_STATIC; StaticSamplerDesc StaticSampler; StaticSampler.Desc.MinFilter = FILTER_TYPE_LINEAR; StaticSampler.Desc.MagFilter = FILTER_TYPE_LINEAR; StaticSampler.Desc.MipFilter = FILTER_TYPE_LINEAR; StaticSampler.TextureName = "g_MutableTexture"; Attrs.Desc.NumStaticSamplers = 1; Attrs.Desc.StaticSamplers = &StaticSampler; ShaderMacroHelper Macros; Macros.AddShaderMacro("USE_SHADOWS", 1); Macros.AddShaderMacro("NUM_SHADOW_SAMPLES", 4); Macros.Finalize(); Attrs.Macros = Macros; RefCntAutoPtr<IShader> pShader; m_pDevice->CreateShader( Attrs, &pShader );
        Creating the Pipeline State Object
        After all required shaders are created, the rest of the fields of the PipelineStateDesc structure provide depth-stencil, rasterizer, and blend state descriptions, the number and format of render targets, input layout format, etc. For instance, rasterizer state can be described as follows:
        PipelineStateDesc PSODesc; RasterizerStateDesc &RasterizerDesc = PSODesc.GraphicsPipeline.RasterizerDesc; RasterizerDesc.FillMode = FILL_MODE_SOLID; RasterizerDesc.CullMode = CULL_MODE_NONE; RasterizerDesc.FrontCounterClockwise = True; RasterizerDesc.ScissorEnable = True; RasterizerDesc.AntialiasedLineEnable = False; Depth-stencil and blend states are defined in a similar fashion.
        Another important thing that pipeline state object encompasses is the input layout description that defines how inputs to the vertex shader, which is the very first shader stage, should be read from the memory. Input layout may define several vertex streams that contain values of different formats and sizes:
        // Define input layout InputLayoutDesc &Layout = PSODesc.GraphicsPipeline.InputLayout; LayoutElement TextLayoutElems[] = {     LayoutElement( 0, 0, 3, VT_FLOAT32, False ),     LayoutElement( 1, 0, 4, VT_UINT8, True ),     LayoutElement( 2, 0, 2, VT_FLOAT32, False ), }; Layout.LayoutElements = TextLayoutElems; Layout.NumElements = _countof( TextLayoutElems ); Finally, pipeline state defines primitive topology type. When all required members are initialized, a pipeline state object can be created by IRenderDevice::CreatePipelineState() method:
        // Define shader and primitive topology PSODesc.GraphicsPipeline.PrimitiveTopologyType = PRIMITIVE_TOPOLOGY_TYPE_TRIANGLE; PSODesc.GraphicsPipeline.pVS = pVertexShader; PSODesc.GraphicsPipeline.pPS = pPixelShader; PSODesc.Name = "My pipeline state"; m_pDev->CreatePipelineState(PSODesc, &m_pPSO); When PSO object is bound to the pipeline, the engine invokes all API-specific commands to set all states specified by the object. In case of Direct3D12 this maps directly to setting the D3D12 PSO object. In case of Direct3D11, this involves setting individual state objects (such as rasterizer and blend states), shaders, input layout etc. In case of OpenGL, this requires a number of fine-grain state tweaking calls. Diligent Engine keeps track of currently bound states and only calls functions to update these states that have actually changed.
        Binding Shader Resources
        Direct3D11 and OpenGL utilize fine-grain resource binding models, where an application binds individual buffers and textures to certain shader or program resource binding slots. Direct3D12 uses a very different approach, where resource descriptors are grouped into tables, and an application can bind all resources in the table at once by setting the table in the command list. Resource binding model in Diligent Engine is designed to leverage this new method. It introduces a new object called shader resource binding that encapsulates all resource bindings required for all shaders in a certain pipeline state. It also introduces the classification of shader variables based on the frequency of expected change that helps the engine group them into tables under the hood:
        Static variables (SHADER_VARIABLE_TYPE_STATIC) are variables that are expected to be set only once. They may not be changed once a resource is bound to the variable. Such variables are intended to hold global constants such as camera attributes or global light attributes constant buffers. Mutable variables (SHADER_VARIABLE_TYPE_MUTABLE) define resources that are expected to change on a per-material frequency. Examples may include diffuse textures, normal maps etc. Dynamic variables (SHADER_VARIABLE_TYPE_DYNAMIC) are expected to change frequently and randomly. Shader variable type must be specified during shader creation by populating an array of ShaderVariableDesc structures and initializing ShaderCreationAttribs::Desc::VariableDesc and ShaderCreationAttribs::Desc::NumVariables members (see example of shader creation above).
        Static variables cannot be changed once a resource is bound to the variable. They are bound directly to the shader object. For instance, a shadow map texture is not expected to change after it is created, so it can be bound directly to the shader:
        PixelShader->GetShaderVariable( "g_tex2DShadowMap" )->Set( pShadowMapSRV ); Mutable and dynamic variables are bound via a new Shader Resource Binding object (SRB) that is created by the pipeline state (IPipelineState::CreateShaderResourceBinding()):
        m_pPSO->CreateShaderResourceBinding(&m_pSRB); Note that an SRB is only compatible with the pipeline state it was created from. SRB object inherits all static bindings from shaders in the pipeline, but is not allowed to change them.
        Mutable resources can only be set once for every instance of a shader resource binding. Such resources are intended to define specific material properties. For instance, a diffuse texture for a specific material is not expected to change once the material is defined and can be set right after the SRB object has been created:
        m_pSRB->GetVariable(SHADER_TYPE_PIXEL, "tex2DDiffuse")->Set(pDiffuseTexSRV); In some cases it is necessary to bind a new resource to a variable every time a draw command is invoked. Such variables should be labeled as dynamic, which will allow setting them multiple times through the same SRB object:
        m_pSRB->GetVariable(SHADER_TYPE_VERTEX, "cbRandomAttribs")->Set(pRandomAttrsCB); Under the hood, the engine pre-allocates descriptor tables for static and mutable resources when an SRB objcet is created. Space for dynamic resources is dynamically allocated at run time. Static and mutable resources are thus more efficient and should be used whenever possible.
        As you can see, Diligent Engine does not expose low-level details of how resources are bound to shader variables. One reason for this is that these details are very different for various APIs. The other reason is that using low-level binding methods is extremely error-prone: it is very easy to forget to bind some resource, or bind incorrect resource such as bind a buffer to the variable that is in fact a texture, especially during shader development when everything changes fast. Diligent Engine instead relies on shader reflection system to automatically query the list of all shader variables. Grouping variables based on three types mentioned above allows the engine to create optimized layout and take heavy lifting of matching resources to API-specific resource location, register or descriptor in the table.
        This post gives more details about the resource binding model in Diligent Engine.
        Setting the Pipeline State and Committing Shader Resources
        Before any draw or compute command can be invoked, the pipeline state needs to be bound to the context:
        m_pContext->SetPipelineState(m_pPSO); Under the hood, the engine sets the internal PSO object in the command list or calls all the required native API functions to properly configure all pipeline stages.
        The next step is to bind all required shader resources to the GPU pipeline, which is accomplished by IDeviceContext::CommitShaderResources() method:
        m_pContext->CommitShaderResources(m_pSRB, COMMIT_SHADER_RESOURCES_FLAG_TRANSITION_RESOURCES); The method takes a pointer to the shader resource binding object and makes all resources the object holds available for the shaders. In the case of D3D12, this only requires setting appropriate descriptor tables in the command list. For older APIs, this typically requires setting all resources individually.
        Next-generation APIs require the application to track the state of every resource and explicitly inform the system about all state transitions. For instance, if a texture was used as render target before, while the next draw command is going to use it as shader resource, a transition barrier needs to be executed. Diligent Engine does the heavy lifting of state tracking.  When CommitShaderResources() method is called with COMMIT_SHADER_RESOURCES_FLAG_TRANSITION_RESOURCES flag, the engine commits and transitions resources to correct states at the same time. Note that transitioning resources does introduce some overhead. The engine tracks state of every resource and it will not issue the barrier if the state is already correct. But checking resource state is an overhead that can sometimes be avoided. The engine provides IDeviceContext::TransitionShaderResources() method that only transitions resources:
        m_pContext->TransitionShaderResources(m_pPSO, m_pSRB); In some scenarios it is more efficient to transition resources once and then only commit them.
        Invoking Draw Command
        The final step is to set states that are not part of the PSO, such as render targets, vertex and index buffers. Diligent Engine uses Direct3D11-syle API that is translated to other native API calls under the hood:
        ITextureView *pRTVs[] = {m_pRTV}; m_pContext->SetRenderTargets(_countof( pRTVs ), pRTVs, m_pDSV); // Clear render target and depth buffer const float zero[4] = {0, 0, 0, 0}; m_pContext->ClearRenderTarget(nullptr, zero); m_pContext->ClearDepthStencil(nullptr, CLEAR_DEPTH_FLAG, 1.f); // Set vertex and index buffers IBuffer *buffer[] = {m_pVertexBuffer}; Uint32 offsets[] = {0}; Uint32 strides[] = {sizeof(MyVertex)}; m_pContext->SetVertexBuffers(0, 1, buffer, strides, offsets, SET_VERTEX_BUFFERS_FLAG_RESET); m_pContext->SetIndexBuffer(m_pIndexBuffer, 0); Different native APIs use various set of function to execute draw commands depending on command details (if the command is indexed, instanced or both, what offsets in the source buffers are used etc.). For instance, there are 5 draw commands in Direct3D11 and more than 9 commands in OpenGL with something like glDrawElementsInstancedBaseVertexBaseInstance not uncommon. Diligent Engine hides all details with single IDeviceContext::Draw() method that takes takes DrawAttribs structure as an argument. The structure members define all attributes required to perform the command (primitive topology, number of vertices or indices, if draw call is indexed or not, if draw call is instanced or not, if draw call is indirect or not, etc.). For example:
        DrawAttribs attrs; attrs.IsIndexed = true; attrs.IndexType = VT_UINT16; attrs.NumIndices = 36; attrs.Topology = PRIMITIVE_TOPOLOGY_TRIANGLE_LIST; pContext->Draw(attrs); For compute commands, there is IDeviceContext::DispatchCompute() method that takes DispatchComputeAttribs structure that defines compute grid dimension.
        Source Code
        Full engine source code is available on GitHub and is free to use. The repository contains two samples, asteroids performance benchmark and example Unity project that uses Diligent Engine in native plugin.
        AntTweakBar sample is Diligent Engine’s “Hello World” example.

         
        Atmospheric scattering sample is a more advanced example. It demonstrates how Diligent Engine can be used to implement various rendering tasks: loading textures from files, using complex shaders, rendering to multiple render targets, using compute shaders and unordered access views, etc.

        Asteroids performance benchmark is based on this demo developed by Intel. It renders 50,000 unique textured asteroids and allows comparing performance of Direct3D11 and Direct3D12 implementations. Every asteroid is a combination of one of 1000 unique meshes and one of 10 unique textures.

        Finally, there is an example project that shows how Diligent Engine can be integrated with Unity.

        Future Work
        The engine is under active development. It currently supports Windows desktop, Universal Windows and Android platforms. Direct3D11, Direct3D12, OpenGL/GLES backends are now feature complete. Vulkan backend is coming next, and support for more platforms is planned.
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