20/04/2020

The Crit Path to Deferred Shading

I need to get this deferred shading thing under wraps, so I've constructed the MVP Critical Pathway to Success! Ooh, fancy 😮

According to Learn OpenGL (opens new window), I only require the following data to light a fragment with forward rendering, verbatim:

• A 3D world-space position vector to calculate the (interpolated) fragment position variable used for lightDir and viewDir.
• An RGB diffuse color vector also known as albedo.
• A 3D normal vector for determining a surface's slope.
• A specular intensity float.
• All light source position and color vectors.
• The player or viewer's position vector.

I can use that exact same data to create a few goemetry buffers containing the rasterised position, normal, albedo, and specular data for the whole scene. Using the same lighting calculation with the new G-buffer input data, I can shade the whole scene, render it to a texture, and display it on a quad. That's the goal. To get there from where I currently am, I'll need a critical path.

Critical Path

1. Coordinate System
   • Entity object to encapsulate a Transform component and Renderer data.
   • Camera component to handle view projection transforms, and move around the scene.
   • The nalgebra-glm (opens new window) crate has all the required math funcionality.
2. Forward Lighting
   • Light component to with color, strength, and type (directional or spotlight).
   • Material component to encapsulate ambient, diffues, specular, and shininess values.
   • Create a GLSL function to calculate lighting from a material's values and all the light source values.
3. Geometry
   • I'm going to skip model loading for now, and just use some pre-defined cube vertex data.
   • Maybe I'll render the light sources as little spheres.
4. Deferred Shading
   • I will need to learn how to use framebuffers.
   • I might need to do something with the Depth buffer.
   • I will need to learn about Multiple Render Targets (MRT).
   • Update the lighting calculation to take input from the G-buffer framebuffer.
5. Profit?
   • Well, no, but, minimum viable product? Yes.