//
// Shader to render floors/ceilings.
//Currently always uses the same texture, will allow lookups in version 2
varying vec2 v_vTexcoord;
varying vec4 v_vColour;

uniform float u_floorProps[6*512]; //Big ole array
uniform float u_height;
uniform float u_width;
uniform float u_playerX;
uniform float u_playerY;
uniform float u_distPlayer;
uniform sampler2D s_floorTex;

void main()
{
    //Okay, so we currently have two texture coords that are between 0 and 1.
    //from that we need to know what the screen coords were, so we can look shit up

    float X = floor(v_vTexcoord.x * u_width);
    float Y = floor(v_vTexcoord.y * u_height);

    int arrayStart = int(X * 6.0);
    float floorScreenY = u_floorProps[arrayStart];
    float distWall = u_floorProps[arrayStart + 3];
    float floorXWall = u_floorProps[arrayStart + 1];
    float floorYWall = u_floorProps[arrayStart + 2];
    //Set alpha to 0 if this pixel is out of range, otherwise set to 1
    if (Y < floorScreenY)
    {
       discard;
    }

    //Determine the texture co-ords for this fragment
    float currentDist = u_height / (2.0 * floorScreenY - u_height); //you could make a small lookup table for this instead
    float weight = (currentDist - u_distPlayer) / (distWall - u_distPlayer);

    float currentFloorX = weight * floorXWall + (1.0 - weight) * u_playerX;
    float currentFloorY = weight * floorYWall + (1.0 - weight) * u_playerY;
    float floorTexWidth = u_floorProps[arrayStart + 4];
    float floorTexHeight = u_floorProps[arrayStart + 5];

    //okay, this bit is different since we just want UVs, not the exact texture coords
    //that looks dumb as shit, but I think it's correct
    float floorTexX = mod(floor(currentFloorX * floorTexWidth),floorTexWidth);
    float floorTexY = mod(floor(currentFloorY * floorTexHeight),floorTexHeight);
    vec2 floorUV = vec2(floorTexX,floorTexY);
    gl_FragColor = v_vColour * texture2D( s_floorTex, floorUV);
}