Mapbox GL Shaders

This repository contains GL shaders which are shared by Mapbox GL JS and Mapbox GL Native.

Pragmas

Some variables change type depending on their context:

if the variable is the same for all features, we declare it as a uniform
if the variable is different for each feature, we declare it as an attribute (in the vertex shader) and an accompanying varying (in both the vertex and fragment shaders).
if the variable is different for each feature and a function of zoom, we declare several attributes and uniforms then calculate the value using interpolation

We abstract over this functionality using pragmas.

#pragma mapbox: define highp vec4 color

main() {
    #pragma mapbox: initialize highp vec4 color
    ...
    gl_FragColor = color;
}

This program defines a variable within main called color, initialize the value of color, then sets gl_FragColor to the value of color.

Pragmas take the following form.

#pragma mapbox: (define|initialize) (lowp|mediump|highp) (float|vec2|vec3|vec4) {name}

When using pragmas, the following requirements apply.

all pragma-defined variables must have both define and initialize pragmas
define pragmas must be in file scope
initialize pragmas must be in function scope
all pragma-defined variables defined and initialized in the fragment shader must also be defined and initialized in the vertex shader because attributes are not accessible from the fragment shader

The _prelude.fragment.glsl and _prelude.vertex.glsl files are automatically included in all shaders by the compiler.