OpenGL ES Shading Language - Praise for OpenGL ES 30 Programming Guide - page 113

referred to as interpolators). The number of vertex shader outputs supported
by an implementation is given by the gl_MaxVertexOutputVectors
built-in variable (querying for GL_MAX_VERTEX_OUTPUT_COMPONENTS
using glGetIntegerv will provide the number of total component values
rather than the number of vectors). The minimum number of vertex
output vectors that an implementation of OpenGL ES 3.0 can support
is 16. Likewise, the number of fragment shader inputs supported by an
implementation is given by gl_MaxFragmentInputVectors (querying for
GL_MAX_FRAGMENT_INPUT_COMPONENTS using glGetIntegerv will provide
the number of total component values rather than the number of vectors).
The minimum number of fragment input vectors that an implementation
of OpenGL ES 3.0 can support is 15.

Example 5-2 is an example of a vertex shader and a fragment shader with
matching output/input declarations.

Example 5-2 Vertex and Fragment Shaders with Matching Output/Input

Declarations

// Vertex shader
#version 300 es

uniform mat4 u_matViewProjection;

// Vertex shader inputs
layout(location = 0) in vec4 a_position;
layout(location = 1) in vec3 a_color;

// Vertex shader output
out vec3 v_color;

void main(void)
{
gl_Position = u_matViewProjection * a_position;
v_color = a_color;
}

// Fragment shader
#version 300 es
precision mediump float;

// Input from vertex shader
in vec3 v_color;

// Output of fragment shader
layout(location = 0) out vec4 o_fragColor;

(continues)