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OpenGL OpenGL and Xwindows

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I want to write a simple OpenGL app in Xwindows and so I haven't been able to find any examples on how to do it. I can do this in windows using just the winapi so I was hoping to find a similar way to do it under X with out using something like GTK+. Any input would be appreciated, thanks

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There is a nice techpubs article on Sgi.com that is a good way to get started.

OpenGl on SGI

Chapter 3. OpenGL and X: Examples - has some sample code for using xt widgets or just using straight xlib to create an OpenGL Context.

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Xlib is quite painfull. You might want to consider using SDL or GTK to set up the window. These are crossplatform, so you also avoid platform specific code. If you still want to do it with only Xlib, PM me and I will send you the code I use to set up windows for use with OGL (it isn't ready for public release yet :)

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Do a google search for a sample app called glxsimple.c. It's from the book OpenGL Programming for the X Window System by Mark J. Kilgard (the green book). It just sets up a simple opengl window using xlib which isn't too bad if you've worked with the winapi, and it's pretty straight forward.

Hope this helps.

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If you check out NeHe, you might see the NeHeGL GLX basecode on the left side, under the heading 'OpenGL Basecode'. If you want something cross-platform, and you don't mind not being able to do fullscreen toggling in Windows, or changing the current display properties (colour depth, refresh rate, etc.), then you might as well use SDL, but if you're like me, and want a fairly flexible window setup, then that code should help you on your way (I still haven't figured out fullscreen toggling using Xlib, but everything else seems to be working fairly well at the moment).

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Quote:
Disgruntled Gamer:
It just sets up a simple opengl window using xlib which isn't too bad if you've worked with the winapi, and it's pretty straight forward.


yes, the simple examples are straight forward but things like fullscreen are tricky to get right. Unfortunately the Xlib documentation isn't clear about which functions can be called in which window state, it took me lots of trial and error to find out. Sad thing that good documentation, like the OpenGL one, is rare.

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Quote:
Original post by Gorax
(I still haven't figured out fullscreen toggling using Xlib, but everything else seems to be working fairly well at the moment).


I think I'm gonna clean up my rewrite of the glx basecode and release it. The fullscreen toggling in the nehe glx code is a dirty hack that leaks memory :-/

But if you are interested here is what I do:
1. unmap the window
2. change screen resolution with the XF86VidMode extention
3. set the viewport and window location/size to match the resolution
4. grab mouse and keybopard
5. set the redirect_override property of the window*
6. map the window

* this is considered bad practice, but I find it ok. The "right way" to do it is window manager hints.

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Hi nefthy,

I've been wondering myself how you setup a full screen window in xwindows. I would be very interested in seeing your code on how to do it. I have a lot more experience with win32 programming than I do with xwindow programming so the steps you listed aren't that familiar to me. Any further explanation would be greatly appreciated. Also is there an easy way to turn off your mouse pointer in xwindows, like an xwindows version of ShowCursor or something?

DG

[Edited by - Disgruntled Gamer on April 21, 2006 6:20:47 PM]

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As I said I will clean the code up and upload it. As for hiding the mouse pointer, I havent found it yet, but I will hopefully.

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Guest Anonymous Poster
Cool thanks guys, this information is great. Hopfully I can post some progress later tonight.

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Quote:
Original post by Anonymous Poster
Cool thanks guys, this information is great. Hopfully I can post some progress later tonight.


Woops that was me.

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here you go: x11.tgz

Note that some of the comments where ment for the guy who is maintaining the nehe SDK so take them with a grain of salt :)

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Oh, if you have any comments, bug fixes, criticism, feel free to mail me: x11 [at] nefthy [dot] de

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Thanks for posting that Nefthy, I got it running on my linux box and it works great!

I was looking for ways to make a custom mouse pointer just through google and yahoo and I couldn't find anything. Do you know if you can create a custom mouse pointer in xwindows and then just set it to a blank bitmap? Also as I type this I'm watching my screen saver on the linux box and it's running in fullscreen mode with no mouse pointer visible. There must be some way to do it.

Thanks again for the code,
DG

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I don't know how to do it, but you can look at XCreatePixmapCursor, XDefineCursor and XUndefineCursor. If you find a way to do it drop me a line :)

Also you could look at the screensaver sourcecode or maybe at the SDL source.

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Thanks for pointing me in the direction of that XCreatePixmapCursor() function. I managed to get your full screen window to be without a mouse cursor. Here's what I did, I put it just after your XStoreName() call which is right after your XCreateWindow() call.

// make these global for clean up
Pixmap cursor_pixmap;
Cursor blank_cursor;

// these can be local
char cursor_data[32];
Colormap def_colormap;
int screen_num;
XColor any_color;


memset(cursor_data, 0x00, 32); //load it with all zero's so we don't see anything
screen_num = DefaultScreen(dpy); // need this for the next line
def_colormap = DefaultColormap(dpy, screen_num); // ditto
XParseColor(dpy, def_colormap, "red", &any_color); // need this to keep XCreatePixmapCursor happy
cursor_pixmap = XCreatePixmapFromBitmapData(dpy, win, cursor_data, 16, 16, 1, 0, 1); // make our pixmap
blank_cursor = XCreatePixmapCursor(dpy, cursor_pixmap, cursor_pixmap, &any_color, &any_color, 8, 8); // make the blank cursor
XDefineCursor(dpy, win, blank_cursor); // select it into our window



Then delete the cursor in your glneDestroyWindow() function before the XDestroyWindow() call, like this.

XUndefineCursor(dpy, win);
XFreeCursor(dpy, blank_cursor);
XFreePixmap(dpy, cursor_pixmap);



I don't think I can get out of that XParseColor() call since I don't really want any color at all. But XCreatePixmapCursor() seems to choke when you pass it in NULL for the XColor params. I use the same cursor_pixmap for both Pixmap params because the mask is all I really care about, as long as I load the mask with all zero's I won't see any cursor no matter what I put in for the first Pixmap param.

I'll probably just be using the above code unless I somehow become motivated enough to sift through screen saver and SDL source code.

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      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 tutorials, sample applications, asteroids performance benchmark and an example Unity project that uses Diligent Engine in native plugin.
      Atmospheric scattering sample 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, Linux, Android, MacOS, and iOS platforms. Direct3D11, Direct3D12, OpenGL/GLES backends are now feature complete. Vulkan backend is coming next, and Metal backend is in the plan.
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