In this tutorial we incorporate our first shader stage into the 3D pipeline: the pixel shader stage. We also explore some basic example pixel shaders (more heavy-duty stuff to come later).
Video
The tutorial video is on YouTube here.
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- What is a Pixel Shader and why is it used? 0:20
- We want to make color mapping of the triangles in the rendering pipeline configurable
- One way is to use templated function objects (functors) as "plug-in" code
- These functors determine the color of the pixel based on their input
- Refactoring of the
gfx.PutPixel(...) function in Pipeline.h 2:04
- This is where we are ultimately determining the color of the pixel
- Inside the PutPixel function, we want to call a shader object that defines the coloring behavior
- Implementation of the programmable pixel shader stage in the pipeline 3:11
- We template the pipeline class on an
<class Effect>
- We will adjust the definition of the
Vertex class depending on what effect we are using
- We adjust
gfx.PutPixel(...) to take a pixel shader object, and call the function operator with the interpolated Vertex data:
gfx.PutPixel( x,y,effect.ps( iLine ) );
- Changes to the
Pipeline class 5:37
- - The
Pipeline object now holds an Effect object (which holds all shader data and methods)
- - Coding the
Effect class 6:03
- - Coding the
PixelShader class 6:22
- Putting it all together in a new
CubeSkinScene.h class 7:26
- - The code now renders the same scene, but has become completely configurable
- Making a new
Effect: Color Blending 8:31
- The
VertexColorEffect functor will not hold a texture and return interpolated texture coordinates
- Instead, it interpolates colors operating on a
Vec3 object that holds RGB values (we encode the Vertex colors as floats)
- Cube definition now needs to hold color data of each Vertex 10:07
- We need a conversion operator and a conversion constructor to translate between the
Vec3 and Color representation of colors 11:12
- Changes to the
Pipeline class: generalizing Vertex transformations (independent of the pixel shader effect) 11:45
- Adding a static function
GetPlain() in Cube.h to get the Vertex colors 13:39
template<class V>
static IndexedTriangleList<V> GetPlain(float size = 1.0f)
{...}
- Coding the scene class </code>CubeVertexColorScene.h</code> 14:13
- Making a new
Effect: Solid Colors 14:47
- Need to address the issue: we can't store color data in the 8 unique cube vertices
- Solution: make the faces of the cube independent (no shared vertices) 16:22
- - This requires 6 faces x 4 vertices per face = 24 vertices
- Definition of
SolidEffect.h (without interpolation of colors)
- Adding a static function
GetPlainIndependentFaces() to Cube.h to get the 24 vertices 18:15
- Demo 19:19
</code>
- Reflections on this approach to Pixel Shading 19:58
- With our approach, the sky is the limit in terms of adding options/effects to the Pixel Shader
- However, because the whole pipeline is templated, each effect requires a pipeline
- - Adantage of using templates: enables aggressive inlining / compiler optimization
- - Disadvantage: we can't switch effects easily at runtime
- There are differences between this approach and how Hardware 3D APIs (like Direct3D and OpenGL) implement this flexibility
- - These let you switch components (e.g. by binding a different shader dynamically)
- - Another difference: use of texturing units seperate from the shader object 21:14
Downloads
The GitHub repository for the tutorial code is here.
See also
