attribute vec2 a_position;
attribute vec2 a_texCoord;

uniform vec2 u_resolution;

varying vec2 v_texCoord;

void main() {
    // convert the rectangle from pixels to 0.0 to 1.0
    vec2 zeroToOne = a_position / u_resolution;

    // convert from 0->1 to 0->2
    vec2 zeroToTwo = zeroToOne * 2.0;

    // convert from 0->2 to -1->+1 (clipspace)
    vec2 clipSpace = zeroToTwo - 1.0;

    gl_Position = vec4(clipSpace * vec2(1, -1), 0, 1);

    // pass the texCoord to the fragment shader
    // The GPU will interpolate this value between points.
    v_texCoord = a_texCoord;
}