Minetest post-processing pipeline basics

README.md

Concepts

• RenderStep - a single step in the pipeline, such as running the 3D render, changing state or applying a shader. Each step has a source and a target
  • RenderSource - a source for the step, a set of textures that are used in the step
  • RenderTarget - a target for the step, a framebuffer with one or more attached textures / renderbuffers.
• Pipeline - a sequence of steps and associated objects such as TextBuffers.
• TextureBuffer - an indexed set of textures that you need, you can create up to 254 textures if the driver permits.
  • TextureBuffer is also a RenderSource and a RenderTarget.
  • Normally you have a single texture buffer that all the steps write to and read from
• PostProcessingStep : RenderStep - draws a full-screen quad with given shader, RenderSource and RenderTarget.

Adding a post-processing step

The pipeline is located in secondstage.cpp.

In order to add a post-processing step:

1. If you need extra textures, add them to the buffer:

• Declare TEXTURE_XXX constant
• Add buffer->setTexture(TEXTURE_XXX, scale, "<some meaningful name>", video::ECF_A8R8G8B8); to register a texture

2. Create shader code in GLSL:

• In client/shaders at the project root, create folder for your shader, for example, depth_of_field.
• Add vertex and fragment shader code to the depth_of_field folder:
  • opengl_vertex.glsl - use code from second_stage/opengl_vertex.glsl
  • opengl_fragment.glsl - start with code from second_stage/opengl_fragment.glsl

3. Set up the postprocessing step:

• Request a shader with the following code:

IWritableShaderSource *s = client->getShaderSource();
  u32 shader_index = s->getShader(
  		"depth_of_field", // name of the folder with the shader code
  		TILE_MATERIAL_BASIC, // material parameter
  		NDT_NORMAL); // node draw type parameter
  video::E_MATERIAL_TYPE shader = s->getShaderInfo(shader_index).material;

• Add the step

RenderStep *effect = pipeline->addStep<PostProcessingStep>(
    shader, // ID of the shader renderer
    std::vector<u8> { TEXTURE_XXX, ... }); // IDs of the textures in the buffer to map to samplers 0, 1, 2 ...
  effect->setRenderSource(buffer);
effect->setRenderTarget(pipeline->createOwned<TextureBufferOutput>(buffer, TEXTURE_YYY)

Note: Make sure all steps are wired to the correct textures. Note: Make sure that the final step is returned from the method, so it's output is routed to the screen later.