#version 410

in float partSlot;
in vec2 xy;
in vec2 uv;

out vec2 uvV;
out float alphaV;
out vec4 colorV;
uniform sampler2D partValues;
uniform float partIndex_translate; // vec4 as x, y, z, scale
uniform float partIndex_color; // vec4 as x, y, z, scale
uniform vec2 meScreenSize;

void main(void)
{
    vec4 partTranslate = texture(partValues, vec2(partIndex_translate, partSlot));

    // Draw against the very back of the visible cube.
    vec4 pos = vec4(xy.x, xy.y, partTranslate.z, 1.0);
    pos.xy /= meScreenSize;
    pos.xy = pos.xy * 2.0 - vec2(1.0, 1.0); // convert from [0,1] to [-1,+1]
    pos.y = -pos.y;
    gl_Position = pos;
    
    uvV = uv;
    colorV = texture(partValues, vec2(partIndex_color, partSlot));
}