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OpenGL Unable to load 2D texture

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Hi all, I have a code I put together from Nehe texture tutorial and glEnable2D and glDisable2D code snippets to try and learn how to do 2D in OpenGL. The problem is, for some reason, I keep getting just the Quad(white rect) and no texture. Here is the code(in C# but similar to C++): Initialize
        protected virtual void Initialize()
        {
            InitEvents();
            // Texture
            textureName = "011-PortTown01.png";
            // Set the Frames per second.
            Events.Fps = 60;
            // Sets Window icon and title
            this.SetWindowAttributes();
            // Creates SDL.NET Surface to hold an OpenGL scene
            screen = Video.SetVideoMode(width, height, true, true, false, true);
            // Reset The Current Viewport
            Gl.glViewport(0, 0, width, height);
            // Load Textures
            LoadTextures();
            // Render Screen
            RenderScreen();
        }



LoadTexture
        /// <summary>
        /// Load Textures
        /// </summary>
        private void LoadTextures()
        {
            // Load Bitmap
            Bitmap textureImage = new Bitmap(textureName);
            // Check For Errors, If Bitmap's Not Found, Quit
            if (textureImage != null)
            {
                // Create The Texture
                Gl.glGenTextures(1,out texture);
                textureImage.RotateFlip(RotateFlipType.RotateNoneFlipY);
                // Flip The Bitmap Along The Y-Axis
                // Rectangle For Locking The Bitmap In Memory
                Rectangle rectangle =
                    new Rectangle(0, 0, textureImage.Width, textureImage.Height);
                // Get The Bitmap's Pixel Data From The Locked Bitmap
                BitmapData bitmapData =
                    textureImage.LockBits(rectangle, ImageLockMode.ReadOnly, PixelFormat.Format24bppRgb);

                // Typical Texture Generation Using Data From The Bitmap
                Gl.glBindTexture(Gl.GL_TEXTURE_2D, texture);
                Gl.glTexImage2D(Gl.GL_TEXTURE_2D, 0, Gl.GL_RGB8, textureImage.Width, textureImage.Height, 0, Gl.GL_BGR, Gl.GL_UNSIGNED_BYTE, bitmapData.Scan0);
                // Fix image for resoulution
                Gl.glTexParameteri(Gl.GL_TEXTURE_2D, Gl.GL_TEXTURE_MIN_FILTER, Gl.GL_LINEAR);
                Gl.glTexParameteri(Gl.GL_TEXTURE_2D, Gl.GL_TEXTURE_MAG_FILTER, Gl.GL_LINEAR);
                Gl.glTexParameterf(Gl.GL_TEXTURE_2D, Gl.GL_TEXTURE_WRAP_S, Gl.GL_REPEAT);
                Gl.glTexParameterf(Gl.GL_TEXTURE_2D, Gl.GL_TEXTURE_WRAP_T, Gl.GL_REPEAT);
                // If Texture Exists
                if (textureImage != null)
                {
                    // Unlock The Pixel Data From Memory
                    textureImage.UnlockBits(bitmapData);
                    // Dispose The Bitmap
                    textureImage.Dispose();
                }

            }
        }




Render
        /// <summary>
        /// Render the screen.
        /// </summary>
        protected virtual void RenderScreen()
        {
            Gl.glEnable(Gl.GL_TEXTURE_2D);
            Gl.glClear(Gl.GL_COLOR_BUFFER_BIT | Gl.GL_DEPTH_BUFFER_BIT);
            Gl.glLoadIdentity();
            // Enable 2D
            Enable2D();
            // Create Texture
            Gl.glGenTextures(1, out texture);
            // Enable GL
            Gl.glTexEnvf(Gl.GL_TEXTURE_ENV, Gl.GL_TEXTURE_ENV_MODE, Gl.GL_REPLACE);
            Gl.glTexEnvf(Gl.GL_TEXTURE_ENV, Gl.GL_TEXTURE_ENV_MODE, Gl.GL_BLEND);
            Gl.glTexEnvf(Gl.GL_TEXTURE_ENV, Gl.GL_TEXTURE_ENV_MODE, Gl.GL_MODULATE);
            Gl.glBindTexture(Gl.GL_TEXTURE_2D, texture);
            // Begin GL
            Gl.glBegin(Gl.GL_QUADS);
            // Upper Left Corner
            Gl.glTexCoord2d(0, 1024);
            Gl.glVertex2d(0, 0);
            // Lower Left Corner
            Gl.glTexCoord2d(0, 0);
            Gl.glVertex2d(0, 1024);
            // Upper Right Corner
            Gl.glTexCoord2d(256, 1024);
            Gl.glVertex2d(256, 0);
            // Lower Rigt Corner
            Gl.glTexCoord2d(256, 0);
            Gl.glVertex2d(256, 1024);
            // End
            Gl.glEnd();
            // Disable 2D
            Disable2D();
        }

Enable/Disable 2D Rendering
       /// <summary>
        /// Enables 2D Mode
        /// </summary>
        void Enable2D()
        {
            int[] vPort = new int[4];
            Gl.glGetIntegerv(Gl.GL_VIEWPORT, vPort);

            Gl.glMatrixMode(Gl.GL_PROJECTION);
            Gl.glPushMatrix();
            Gl.glLoadIdentity();
            
            Gl.glOrtho(vPort[0], vPort[2], vPort[3], vPort[1], -1, 1);
            Gl.glMatrixMode(Gl.GL_MODELVIEW);
            Gl.glPushMatrix();
            Gl.glLoadIdentity();
        }
        /// <summary>
        /// Disables 2D Mode
        /// </summary>
        void Disable2D()
        {
            Gl.glMatrixMode(Gl.GL_PROJECTION);

            Gl.glPopMatrix();
            Gl.glMatrixMode(Gl.GL_MODELVIEW);
            Gl.glPopMatrix();
        }



That's all I have and I'm not sure what I'm doing wrong here.. [Edited by - mr_mo on June 26, 2008 12:44:40 PM]

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First of all, do you realize that you can't load .png files when you call

Bitmap textureImage = new Bitmap(textureName);

Unless you are calling your texture loading lib Bitmap for all types?

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// Begin GL
Gl.glBegin(Gl.GL_QUADS);
// Upper Left Corner
//Gl.glTexCoord2f(.25F, .125F);
//Gl.glVertex(0.0F, 30.0F, 0.0F);
Gl.glTexCoord2d(0, 1024);
Gl.glVertex2d(0, 0);
// End
Gl.glEnd();

texture coordinates are from 0 to 1. Did you really mean 1024 (repeated textures 1023 times)??

You only have on vertex being drawn for a quad that needs 4 vertcies?

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Thank you for your replies :).

Quote:
Original post by MARS_999
First of all, do you realize that you can't load .png files when you call

Bitmap textureImage = new Bitmap(textureName);

Unless you are calling your texture loading lib Bitmap for all types?


I'm pretty sure it loads it. Its a .Net class(GDI+) and on top of that, I used it to paint on a form several times. Also, I've checked during debug mode to see if it loaded the pixels.

Quote:
// Begin GL
Gl.glBegin(Gl.GL_QUADS);
// Upper Left Corner
//Gl.glTexCoord2f(.25F, .125F);
//Gl.glVertex(0.0F, 30.0F, 0.0F);
Gl.glTexCoord2d(0, 1024);
Gl.glVertex2d(0, 0);
// End
Gl.glEnd();

texture coordinates are from 0 to 1. Did you really mean 1024 (repeated textures 1023 times)??

You only have on vertex being drawn for a quad that needs 4 vertcies?


No, its seems i somehow deleted rest of the code >.<. My apologies. I've deleted the 3 other coordinates and didn't notice i guess. However, it didn't work with the other 3 corners.

Does Gl.glTexCoord2d(0, 1024) really load the texture 1023 times? The size of the image is (256,1024). So, I was under the impression that it positioned the lower left corner(x,y). I've read that texture coordinates must mirror vertex coordinates and so upper becomes lower and left becomes right, is this right?

I've updated my original post with correct code. I'm sorry for the confusion.

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Quote:
Original post by mr_mo
Quote:
// Begin GL
Gl.glBegin(Gl.GL_QUADS);
// Upper Left Corner
//Gl.glTexCoord2f(.25F, .125F);
//Gl.glVertex(0.0F, 30.0F, 0.0F);
Gl.glTexCoord2d(0, 1024);
Gl.glVertex2d(0, 0);
// End
Gl.glEnd();

texture coordinates are from 0 to 1. Did you really mean 1024 (repeated textures 1023 times)??

You only have on vertex being drawn for a quad that needs 4 vertcies?


<snip>
I've read that texture coordinates must mirror vertex coordinates and so upper becomes lower and left becomes right, is this right?

No? They don't have to, and normally don't if you're trying to see your picture right-side-up. They can, but I don't think you want them to. You may be confusing this with window coordinates (in Windows) and OpenGL's coordinate systems, but that's only on the y axis.

Quote:
I've updated my original post with correct code. I'm sorry for the confusion.

You don't seem to have fixed what dpadam450 pointed out - you really only want to use texture coordinates 0.0 and 1.0. These are the lower and upper values for either edge of your texture, OpenGL could (at this point) care less about what exact texels you want to see, it cares about what fraction of the texture you want to see. Normally, OpenGL will generate mipmaps for you, which throws the idea of "give me texel 'x,y'" right out the window. Instead, you want to say "give me region 'x/width,y/height' of my texture," which will apply the appropriate part of the texture to your primitive. As you can see, this number will usually be in the range 0..1 for values of x and y within the texture. However, specifying a larger number can have different effects. Depending on how you have things set up, it will either repeat the texture, or clamp the value to the edge of the texture. In the latter case, you'll end up with one tiny version of your texture in one corner (lower left if you haven't applied any transformations) with bands extending up and to the right containing the contents of the upper and right edges of the texture, respectively. Once you have it loading correctly, try changing the necessary parameters:
          
Gl.glTexParameterf(Gl.GL_TEXTURE_2D, Gl.GL_TEXTURE_WRAP_S, Gl.GL_CLAMP);
Gl.glTexParameterf(Gl.GL_TEXTURE_2D, Gl.GL_TEXTURE_WRAP_T, Gl.GL_CLAMP);
and you'll see what I mean.

Also, you don't want to call Gl.glGenTextures(1, out texture); every frame, just once when you're loading the texture. It makes space for a new texture object, so you're just leaving the one you already loaded in memory somewhere, and causing texture to point to a newly created empty blob of nothing.

So, for now, change to this and see if it works:

/// <summary>
/// Render the screen.
/// </summary>
protected virtual void RenderScreen()
{
Gl.glEnable(Gl.GL_TEXTURE_2D);
Gl.glClear(Gl.GL_COLOR_BUFFER_BIT | Gl.GL_DEPTH_BUFFER_BIT);
Gl.glLoadIdentity();
// Enable 2D
Enable2D();
// Create Texture
// Note: this doesn't create a texture, just reserves space for one.
// since you never come back and create one, you're applying a blank texture.
// Gl.glGenTextures(1, out texture);
// Enable GL
// Note: these are for testing, I guess? You don't need them here, especially since the first overrides the first two....
Gl.glTexEnvf(Gl.GL_TEXTURE_ENV, Gl.GL_TEXTURE_ENV_MODE, Gl.GL_REPLACE);
Gl.glTexEnvf(Gl.GL_TEXTURE_ENV, Gl.GL_TEXTURE_ENV_MODE, Gl.GL_BLEND);
Gl.glTexEnvf(Gl.GL_TEXTURE_ENV, Gl.GL_TEXTURE_ENV_MODE, Gl.GL_MODULATE);
Gl.glBindTexture(Gl.GL_TEXTURE_2D, texture);
// Begin GL
Gl.glBegin(Gl.GL_QUADS);
// Upper Left Corner - (actually lower left, you seem to have flipped everything in Y)
Gl.glTexCoord2d(0, 0);
Gl.glVertex2d(0, 0);
// Upper Right Corner - (again, actually lower right)
Gl.glTexCoord2d(1, 0);
Gl.glVertex2d(256, 0);
// Lower Left Corner
// Does this winding produce a proper quad? I've never tried drawing a quad out of order before...
// Usually, the ordering of vertices for a quad is to just trace around the perimeter counter-clockwise (in OpenGL)
// i.e. ll, lr, ur, ul
Gl.glTexCoord2d(0, 1);
Gl.glVertex2d(0, 1024);
// Lower Rigt Corner
Gl.glTexCoord2d(1, 0);
Gl.glVertex2d(256, 1024);
// End
Gl.glEnd();
// Disable 2D
Disable2D();
}


If it still doesn't work, try swapping the last two vertex/texcoord pairs to have the indicated winding. If it still doesn't work, post back! [smile]

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Oh sorry, I didn't mean I corrected the code, just re-added the parts that were deleted.

So, I added the code you gave me, didn't work. Below is what I ended up with:


protected virtual void RenderScreen()
{
// Enable GL
Gl.glEnable(Gl.GL_TEXTURE_2D);
Gl.glClear(Gl.GL_COLOR_BUFFER_BIT | Gl.GL_DEPTH_BUFFER_BIT);
Gl.glLoadIdentity();
// Enable 2D
Enable2D();
// Add Texture
Gl.glTexEnvf(Gl.GL_TEXTURE_ENV, Gl.GL_TEXTURE_ENV_MODE, Gl.GL_REPLACE);
Gl.glBindTexture(Gl.GL_TEXTURE_2D, texture);
// Begin GL
Gl.glBegin(Gl.GL_QUADS);
// i.e. ll, lr, ur, ul
// Lower Left Corner
Gl.glTexCoord2d(0, 1);
Gl.glVertex2d(0, 1024);
// Lower Rigt Corner
Gl.glTexCoord2d(1, 0);
Gl.glVertex2d(256, 1024);
// Upper Right Corner
Gl.glTexCoord2d(1, 0);
Gl.glVertex2d(256, 0);
// Upper Left Corner
Gl.glTexCoord2d(0, 0);
Gl.glVertex2d(0, 0);
// End
Gl.glEnd();
// Disable 2D
Disable2D();
}





Oh, and thanks for the heads up on the order of things. I knew there was a specific order, but I couldn't figure out what it was.

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Quote:
Original post by mr_mo
Oh sorry, I didn't mean I corrected the code, just re-added the parts that were deleted.

So, I added the code you gave me, didn't work.
By "didn't work," I assume you mean you got the same white quad?

Quote:
Below is what I ended up with:

My fault on this one, I made a typo -

// Lower Rigt Corner
Gl.glTexCoord2d(1, 0);
Gl.glVertex2d(256, 1024);

should be

// Lower Rigt Corner
Gl.glTexCoord2d(1, 1);
Gl.glVertex2d(256, 1024);

I think I know now why you thought texcoords and vertices should be "mirrored" - because they should be in most cases! But not mirrored as in "flipped," mirrored as in "the same." So, when your x coord is at its max (256), so should the s (or u, depending on nomenclature) texcoord (1). So, wherever you have a 256 or 1024, use 1 for the texcoord.

This shouldn't fix it, though, unless you got more than just a white square. This mistake would have caused a wonky texture to be applied...

The next step is to include error checking. I'm not sure what needs to be done to get it to C# land, but the basic idea is to use glGetError after any important calls, and make sure you haven't broken something without knowing it.

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Edit:
My mistake, there is no error. I added Check error between begin and end, so it gave the Invalid operation.

So there is no error and the problem(white quad, not tex) still persists. I added CheckError(Gl.glGetError()), which cases the error type, after everyline that uses OpenGL .


[Edited by - mr_mo on June 26, 2008 6:24:26 PM]

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Allright, two more things to try. First, and easier, use a power of 2 x power of 2 (64x64, 512x512, etc.) texture. Second, tell GL to build mipmaps for you with gluBuild2DMipmaps instead of glTexImage2D. Then you'll want to use GL_LINEAR_MIPMAP_LINEAR as your minification filter.

Crossing fingers.

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Don't use gluBuild2DMipmaps if your card supports GPU(hardware acclerated mipmap creation) use this instead, as long as its a POT texture, unless your Gfx has NPOT support.

glTexParameteri(GL_TEXTURE_2D, GL_GENERATE_MIPMAP_SGIS, GL_TRUE);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB8, textureImage.Width, textureImage.Height, 0, GL_BGR, Gl.GL_UNSIGNED_BYTE, bitmapData.Scan0);


BTW what hardware are you on, are you sure your card or drivers are current? GL_BGR isn't supported on GL versions less than 1.2 or 1.3? Can't remember which one...

One last thing just for dumb luck try making that texture image as a .bmp not a .png

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Thank you for the help.
I've tested the texture I use with NeHe Lesson 06(C# version) and the texture works fine.

I've also tried gluBuild2DMipmaps as well but nope. I'm looking at a working 2D texture source but I just can't figure out what I'm missing. I might have to start from scratch using that as a guide, which I don't mind.

Btw, can I use particles in 2D? or must I disable 2D and then enable 3D?

Edit:
I got it to work :D. Thanks for all your help guys :).

[Edited by - mr_mo on June 29, 2008 6:01:00 PM]

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      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.
    • By michaeldodis
      I've started building a small library, that can render pie menu GUI in legacy opengl, planning to add some traditional elements of course.
      It's interface is similar to something you'd see in IMGUI. It's written in C.
      Early version of the library
      I'd really love to hear anyone's thoughts on this, any suggestions on what features you'd want to see in a library like this? 
      Thanks in advance!
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