3D Fundamentals Tutorial 9

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.

• 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 </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

• Planet Chili Patreon
• Next in series (Tutorial 10)
• 3D Fundamentals Series