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OpenGL Changing Hue of a texture

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Everyone knows how do the color themes change in Winamp3+. I would like to implement something simillar in my game. The problem is that i dont know how to change the hue of a texture in OpenGL. I tried glColor3f to change the color of the poly that wears my texture, but that doesn't actualy change the hue, it changes the whole color (even the regions of the texture that shouldn't change at all (white and grey)). In Photoshop you can also change the hue of an image by simply adding a coloured layer over the image, and setting it's blending mode to "Hue". I also tried that one in OpenGl, but i couldn't find a blending mode that suits my needs. Is there any solution? Thanks in advance.

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James is correct. Unfortunately in this case, the hue of a color is computed with all three of the individual color components. In OpenGL, I have found, there is no way to perform any operation which takes into account all three of the color components at the same time. Each color component is handled separately.

There is, however, one exception to this rule that I have found which may solve your problem: Pixel Shaders. A pixel shader can do a number of very complicated pixel operations on the hardware level. This means you don't have to perform the relatively slow conversions James discussed, but the drawback is that pixel shaders are relatively new technology (introduced in December of 2001, I believe) and if you are going for backwards-compatibility in your game, you may find it tough to do with pixel shaders. Furthermore, while NVidia provides a pixel shader package with tools to ease learning, it is still a new technology that you will need to take time to learn if you so choose.

If this is what you want, however, you may consider visiting http://www.nvidia.com/object/feature_pixelshader.html for more information.

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I'm a beginner in C++ and OpenGL, so i think it's too early for me to get into shader details.

I've got the functions that transform RGB->HSB and HSB->RGB. The process of loading a texture from a file(tga in my case) stores the image data to the memory, pixel by pixel. Maybe i can load all that data and change the hue of that texture, pixel by pixel, and then save it as another texture?

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That doesn't sound unreasonable. However, unless I've misunderstood, it sounds like you could optimize your texture loading routine. This is how I would do it:


1. Open the file, and read the tga headers to get the texture dimensions and bit depth.
2. Read in the actual image data all at once.
3. Loop through all the pixels
3.1. Convert the pixel to HSV
3.2. Change the hue
3.3. Convert the pixel back to RGB

Usually, when loading .tga files into OpenGL you would loop through all the pixels to convert from the .tga's BGR representation to RGB anyway. It's probably not too expensive to add the hue change, since you're doing it at loading time anyway.

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Ok. That's almost what i was talking about. But is it possible to get the image data of the texture after it was allready loaded. (For example i need "real_time hue changing"). And if it is possible, where do i get it from?
Thanks.

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Quote:
Original post by Devil_Inside
Ok. That's almost what i was talking about. But is it possible to get the image data of the texture after it was allready loaded. (For example i need "real_time hue changing"). And if it is possible, where do i get it from?
Thanks.
glGetTexImage will get the texture data from OpenGL for you. It's pretty slow though because it is reading the data from the video card (that's most likely where the texture is stored). It's better to just keep a copy of the data in system memory and edit that, then update the texture with glTexSubImage2D.

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I'm pretty sure you can use the material to modify the color of a texture, in how it shows up. If you have a texture which is black and white stripes, with no set material (or a white material), and then you change the material to one colors 255,0,0 and then render the same texture you will end up with red and black stripes.

Basicly what it does is multiply (in a 0.0 to 1.0 range) the color of the texture with the color of the material. White (1.0) multipled by any material ends up the material color. Black (0.0) multipled by any material ends up black. Things in between end up something in between.

The most obvious example fo this that I can think of is the armor in EverQuest used the Direct3D equiv of this. Base armor was a white/silver/black detail. Then different actual equipment had a material color associated with it. A user could switch between a red BP and blue BP, and while the color would change, the detailing would remain identicial.

This became most interesting with some of the robes, which were not a base white color. When you multiply a texture of pink and purble stripes and peach detail by 0,200,200 you end up with a very different look then when you multiple the same texture by 200,200,0 or 50,255,50.


If you want to use 'Hue' though you must still convert from HSV to RGB. But you don't need to do it every pixel. Convert once, set material to that color.


edit: In retrospect I think I completly missed the point of the question, huh. If you want white and grey areas to not be effected you have to do it entirly yourself, either by changing the texture by hand or pixel shaders.

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Ok, that's what i tried:
1. I duplicated my LoadTgaTexture() function and modified it so it doesn't create a texture after it loads the data from the file, but saves the data to a special structure;
2. I created a function that loops through the pixels of the image from the structure and changes their color.
3. I created a function that updates the old data of the texture with the new, modified data (using glTexSubImage2d).

Everything works fine except one thing. glTexSubImage2D aplies my new texture with its width and height smaller than the original texture. This way only a part of the original textures gets updated. And the strange thing is that the updated part contains the whole texture, but in a smaller scale. I don't understand how could this be, if the new texture has the old's texture width and height and the same number of pixels. It should fit just right, but it doesn't. Where could be the problem?

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void UpdateTexture(TGADATA *tgafile, int TexId)
{
glBindTexture(GL_TEXTURE_2D,TextureArray[TexId]);
int format;
if(tgafile->channel==4) format=GL_RGBA; else format=GL_RGB;
glTexSubImage2D(GL_TEXTURE_2D, 0, 0, 0, tgafile->width, tgafile->height, format, GL_UNSIGNED_BYTE, tgafile->data);
};

Here is the code. The other strange thing is that if i recreate the texture using:


gluBuild2DMipmaps(GL_TEXTURE_2D, tgafile->channel, tgafile->width, tgafile->height, TextureType, GL_UNSIGNED_BYTE, tgafile->data);

for example, it works fine, fullsize.

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Guest Anonymous Poster
I think the ARB_imaging extension can do this. IIRC, You can convolve the colour of a fragment with a matrix. It's not in the OpenGL core specification - at least in 1.2 it's optional, so ideally you'd need a fallback path.

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Quote:
Original post by Devil_Inside

void UpdateTexture(TGADATA *tgafile, int TexId)
{
glBindTexture(GL_TEXTURE_2D,TextureArray[TexId]);
int format;
if(tgafile->channel==4) format=GL_RGBA; else format=GL_RGB;
glTexSubImage2D(GL_TEXTURE_2D, 0, 0, 0, tgafile->width, tgafile->height, format, GL_UNSIGNED_BYTE, tgafile->data);
};

Well, I can't see anything wrong with the code.

Quote:


gluBuild2DMipmaps(GL_TEXTURE_2D, tgafile->channel, tgafile->width, tgafile->height, TextureType, GL_UNSIGNED_BYTE, tgafile->data);

for example, it works fine, fullsize.


Well, then apparently it's got something to do with the mipmapping. I can't tell you exactly what, it's a little strange. Maybe you have to upload the texture data for each of the mipmap leves individually with glTexSubImage2D...

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The other thing i noticed today is that i cant use glTexImage2D to create 32bit textures. The 32bit textures created using glTexImage2D are represented as white boxes (24bit textures are ok) while gluBuild2DMipmaps() works fine with both 32 and 24 bit.

That's what works:

glGenTextures(1,&TextureArray[TextureID]);
glBindTexture(GL_TEXTURE_2D,TextureArray[TextureID]);
int TextureType;
if(tgafile->channel==4) TextureType=GL_RGBA; else TextureType=GL_RGB;
gluBuild2DMipmaps(GL_TEXTURE_2D, tgafile->channel, tgafile->width, tgafile->height, TextureType, GL_UNSIGNED_BYTE, tgafile->data);
glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_NEAREST);
glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MAG_FILTER, GL_LINEAR_MIPMAP_LINEAR);


And that's what doesn't work:

glGenTextures(1,&TextureArray[TextureID]);
glBindTexture(GL_TEXTURE_2D,TextureArray[TextureID]);
int TextureType;
if(tgafile->channel==4) TextureType=GL_RGBA; else TextureType=GL_RGB;
glTexImage2D(GL_TEXTURE_2D,0,tgafile->channel, tgafile->width, tgafile->height, 0, TextureType, GL_UNSIGNED_BYTE, tgafile->data);
glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MIN_FILTER,GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MAG_FILTER,GL_LINEAR);



And about the mipmap levels: how do i know how many levels there are?

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All right!!! I've got the solution to the problem with glTexSubImage2D(). My texture size wasn't "^2", i changed the size and now its updating fullsize.

If i get it right, i don't really need mipmaps if i'm using opengl for 2d games. I can only create level 0 texture and that's all, am i wrong? But the problem with glTexImage2D still exists. Could hardware be the cause of glTexImage2D 32-bit texture creation failure?

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Quote:
Original post by Devil_Inside
All right!!! I've got the solution to the problem with glTexSubImage2D(). My texture size wasn't "^2", i changed the size and now its updating fullsize.


Ah! Sure, that makes sense now.

Quote:

If i get it right, i don't really need mipmaps if i'm using opengl for 2d games. I can only create level 0 texture and that's all, am i wrong?


You're entirely right.

Quote:

But the problem with glTexImage2D still exists. Could hardware be the cause of glTexImage2D 32-bit texture creation failure?

You know, I had a similar problem, (might very well have been the exact same one), a little while ago. There was a case in which glTexImage2D should have worked perfectly fine, but for some reason the texture turned up white. I really had checked everything, (all the parameters were correct, glGetError returned GL_NO_ERROR, the texture had power of two dimensions, and everything...) It worked with gluBuild2DMipmaps, though. I didn't actually look into the problem, so I'm afraid I don't have a solution...

Anyway, congratulations on getting it working.

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      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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