Texture Shading

We've seen shading with a constant color for the entire model, and we've seen shading with a different color for each vertex. Texture mapping enables a different color for each fragment.

This entails the addition of a texture coordinate attribute to the vertex shader, plus a texture coordinate varying to communicate this attribute from the vertex shader to the fragment shader.

〈Vertex Shader〉 ≡
precision mediump float

uniform mat4 projectionMatrix
uniform mat4 viewMatrix
uniform mat4 modelMatrix

attribute vec4 vertexPosition
attribute vec2 vertexTexCoord

varying vec2 fragmentTexCoord

function main()
fragmentTexCoord ← vertexTexCoord
gl_Position ← projectionMatrix · viewMatrix · modelMatrix · vertexPosition

The image reference is then made per-fragment using a sampler uniform.

〈Fragment Shader〉 ≡
precision mediump float

varying vec2 fragmentTexCoord
uniform sampler2D modelTexture

function main()
modelColor ← texture2D(modelTexture, fragmentTexCoord)
gl_FragColor ← modelColor