WebGL Shaders with Alpha

gistfile1.txt

// vertex shader
attribute float a_alpha;
attribute vec2 a_position;
attribute vec2 a_texCoord;

uniform vec2 u_resolution;

varying vec2 v_texCoord;

void main () {
    // normalize and convert to -1 to 1 (clip space)
    vec2 clipSpace = a_position / u_resolution * 2.0 - 1.0;

    // invert y-axis
    gl_Position = vec4(clipSpace * vec2(1, -1), 0, 1);

    v_alpha = a_alpha;
    v_texCoord = a_texCoord;
}

// fragment
precision mediump float;

uniform sampler2D u_image;

varying float v_alpha;
varying vec2 v_texCoord;

void main () {
    vec4 texture = texture2D(u_image, v_texCoord);
    gl_FragColor = vec4(texture.rgb, texture.a * v_alpha);
}