#version 410

uniform sampler2D fontTexture;
uniform sampler2D atlasTexture;
uniform vec2 atlasSize;

in vec4 colorV;
in vec4 highlightColorV;
in vec2 textureUvV; // 0..1 across the terminal window

out vec4 fragColor;


vec3 mf(vec3 x)
{
    return x - floor(x);
}
void main (void)
{
    fragColor = vec4(1,1,1,1);
//    return;
    
    vec2 uv = textureUvV.xy;
    
    // atlasTexture has the character data as ascii/255 in red, atlasSize grid
    
//    uv.y = 1.0 - uv.y;
    uv *= atlasSize;
    vec2 charPart = fract(uv);
    
    uv = (floor(uv) + vec2(0.5, 0.5)) / atlasSize;
    
    // charF == ascii char 0x00 to 0xff.
    vec4 termPixel = texture(atlasTexture, uv);
    
    int byteR = int(termPixel.r * 255.0);
    int byteG = int(termPixel.g * 255.0);
    int byteB = int(termPixel.b * 255.0);
    int byteA = int(termPixel.a * 255.0);
    
    float charF = 256 * byteG + byteR;
    int charColorRrrGggBb = byteA;
    int flags = byteB;
    
    vec4 charColor = vec4(float(charColorRrrGggBb >> 5) / 7.0, float((charColorRrrGggBb >> 2) & 7) / 7.0, float(charColorRrrGggBb & 3) / 3.0, 1.0);
    
    if((flags & 2) != 0)
    {
        // double the font size (show appropriate quarter-char in this cell)
        uv = textureUvV.xy;
        //uv.y = 1.0 - uv.y;
        uv *= (atlasSize / 2.0);
        charPart = fract(uv);
        // TODO: Understand why this hack? I added it on 2016-11-04 but not sure why it became relevant. It makes no sense.
        // Saw bug with half-split big chars. Swapped the left-right halves.
        charPart.x = fract(charPart.x + 0.5);
    }
    
    // let bit indicate highlighting
    vec4 backGround = colorV; // blue transparency
    if((flags & 1) != 0)
        backGround = highlightColorV; // or yellowish if high bit set
    
    // textureFont is a 16 x 64 of char pictures, 0x00..0xff four times.
    
    float characterColumns = 32.0;
    float characterRows = 32.0;
    float characterFirst = 0;
    
    charF -= characterFirst;

    if(charF < 1.0)
        discard;

    float charLeft = mod(charF, characterColumns) / characterColumns;
    float charWidth = 1.0 / characterColumns;
    float charTop = floor(charF / characterColumns) / characterRows;
    float charHeight = 1.0 / characterRows;
    
    charPart = clamp(charPart, 1.0/16.0, 15.0/16.0);
    vec2 charSpot = vec2(charLeft, charTop) + charPart * vec2(charWidth, charHeight);
    float charVal = texture(fontTexture, charSpot).r; // pixel from character
    charVal = pow(charVal, 0.25);
    vec4 c = vec4(charVal, charVal, charVal, charVal); // color is white, premul
    c *= charColor;
    
//    c = max(c, backGround);
    c = mix(backGround, c, charVal);
    

    c.a = 1.0;
    c.a = colorV.a;
    fragColor = c;
}