/*

*/

#version 120
#ifdef GL_ES
precision mediump float;
#endif
#extension GL_EXT_gpu_shader4 : enable

//layout(origin_upper_left) in vec4 gl_FragCoord; // commented; requires #version 150 or later
// gl_FragCoord is origin to bottom-left

varying vec4 v_color;
varying vec2 v_texCoords;
uniform sampler2D u_texture;


uniform vec2 screenDimension;
uniform vec2 tilesInAxes; // size of the tilemap texture; vec2(tiles_in_horizontal, tiles_in_vertical)

uniform sampler2D tilemap; // RGBA8888

uniform sampler2D tilesAtlas; // terrain, wire, fluids, etc.
uniform sampler2D tilesBlendAtlas; // alternative terrain for the weather mix (e.g. yellowed grass)
uniform float tilesBlend = 0.0; // percentage of blending [0f..1f]. 0: draws tilesAtlas, 1: draws tilesBlendAtlas

uniform vec2 tilesInAtlas = vec2(256.0, 256.0);
uniform vec2 atlasTexSize = vec2(4096.0, 4096.0);

vec2 _tilesInAtlas = vec2(1.0, 1.0) / tilesInAtlas;
vec2 tileSizeInPx = atlasTexSize * _tilesInAtlas; // should be like ivec2(16.0, 16.0)
vec2 _tileSizeInPx = vec2(1.0, 1.0) / tileSizeInPx; // should be like ivec2(0.06125, 0.06125)

uniform vec4 colourFilter = vec4(1, 1, 1, 1); // used by WALL to darken it

uniform ivec2 cameraTranslation = ivec2(0, 0); // used to offset the drawing; it's integer because we want the drawing to be pixel-aligned

uniform float drawBreakage = 1.0; // set it to 0f to not draw breakage, 1f to draw it; NEVER set to any other values.

uniform float mulBlendIntensity = 1.0; // used my MUL-blending drawings; works about the same way as the Layer Opacity slider of Photoshop/Krita/etc.

const vec2 bc = vec2(1.0, 0.0); //binary constant

ivec2 getTileXY(int tileNumber) {
    return ivec2(tileNumber % int(tilesInAtlas.x), tileNumber / int(tilesInAtlas.x));
}

// return: int=0xaarrggbb
int _colToInt(vec4 color) {
    return int(color.b * 255) | (int(color.g * 255) << 8) | (int(color.r * 255) << 16) | (int(color.a * 255) << 24);
}

// 0x0rggbb where int=0xaarrggbb
// return: [0..1048575]
int getTileFromColor(vec4 color) {
    return _colToInt(color) & 0xFFFFF;
}

// 0x00r00000 where int=0xaarrggbb
// return: [0..15]
int getBreakageFromColor(vec4 color) {
    return (_colToInt(color) >> 20) & 0xF;
}

void main() {

    // READ THE FUCKING MANUAL, YOU DONKEY !! //
    // This code purposedly uses flipped fragcoord. //
    // Make sure you don't use gl_FragCoord unknowingly! //
    // Remember, if there's a compile error, shader SILENTLY won't do anything //


    // default gl_FragCoord takes half-integer (represeting centre of the pixel) -- could be useful for phys solver?
    // This one, however, takes exact integer by rounding down. //
    vec2 overscannedScreenDimension = tilesInAxes * tileSizeInPx; // how many tiles will fit into a screen; one used by the tileFromMap; we need this because screen size is not integer multiple of the tile size
    vec2 flippedFragCoord = vec2(gl_FragCoord.x, screenDimension.y - gl_FragCoord.y) + cameraTranslation; // NO IVEC2!!; this flips Y

    // get required tile numbers //

    vec4 tileFromMap = texture2D(tilemap, flippedFragCoord / overscannedScreenDimension); // raw tile number
    int tile = getTileFromColor(tileFromMap);
    int breakage = getBreakageFromColor(tileFromMap);
    ivec2 tileXY = getTileXY(tile);
    ivec2 breakageXY = getTileXY(breakage + 5); // +5 is hard-coded constant that depends on the contents of the atlas

    // calculate the UV coord value for texture sampling //

    // don't really need highp here; read the GLES spec
    vec2 uvCoordForTile = (mod(flippedFragCoord, tileSizeInPx) * _tileSizeInPx) * _tilesInAtlas; // 0..0.00390625 regardless of tile position in atlas
    vec2 uvCoordOffsetTile = tileXY * _tilesInAtlas; // where the tile starts in the atlas, using uv coord (0..1)
    vec2 uvCoordOffsetBreakage = breakageXY * _tilesInAtlas;

    // get final UV coord for the actual sampling //

    vec2 finalUVCoordForTile = uvCoordForTile + uvCoordOffsetTile;// where we should be actually looking for in atlas, using UV coord (0..1)
    vec2 finalUVCoordForBreakage = uvCoordForTile + uvCoordOffsetBreakage;

    // blending a breakage tex with main tex //

    vec4 tileCol = texture2D(tilesAtlas, finalUVCoordForTile);
    vec4 tileAltCol = texture2D(tilesBlendAtlas, finalUVCoordForTile);

    vec4 finalTile = mix(tileCol, tileAltCol, tilesBlend);

    vec4 finalBreakage = drawBreakage * texture2D(tilesAtlas, finalUVCoordForBreakage); // drawBreakeage = 0 to not draw, = 1 to draw

    vec4 finalColor =mix(finalTile, finalBreakage, finalBreakage.a) * bc.xxxy + (finalTile * bc.yyyx);

    gl_FragColor = mix(colourFilter, colourFilter * finalColor, mulBlendIntensity);

}