3D Fundamentals Tutorial 9

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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).


The tutorial video is on YouTube here.

  • 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 in the rendering 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 CubeVertexColorScene.h 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
  • Reflections on our 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


The GitHub repository for the tutorial code is here.

See also