#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 tilemapSize;
uniform sampler2D tilemap; // MUST be RGBA8888

uniform sampler2D tilesAtlas;
uniform sampler2D backgroundTexture;

uniform vec2 tileInAtlas = vec2(256, 256);
uniform vec2 atlasTexSize = vec2(4096, 4096);


uniform vec2 tileInDim; // vec2(tiles_in_horizontal, tiles_in_vertical)
uniform vec2 cameraTranslation = vec2(0, 0); // Y-flipped
uniform float tileSizeInPx = 16;



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

void main() {

    // READ THE FUCKING MANUAL, YOU DONKEY !! //
    // Without further code in either GDX or this shader, //
    // Onscreen TILE COORD WILL BE UPSIDE DOWN (bottom first). //
    // This is intended behaviour. //


    vec2 pxCoord = gl_FragCoord.xy + cameraTranslation;

    int tile = 0;// uses usual absolute tile ID for atlas (upper-left); sample from texture2D(tileAtlas, some more code);
    ivec2 tileXY = getTileXY(tile);

    vec2 coordInTile = mod(pxCoord, tileSizeInPx) / tileSizeInPx; // 0..1 regardless of tile position in atlas

    // flip Y of coordInTile //
    coordInTile = vec2(coordInTile.x, 1 - coordInTile.y);

    highp vec2 singleTileSizeInUV = vec2(1) / tileInAtlas; // 0.00390625
    highp vec2 uvCoordForTile = coordInTile * singleTileSizeInUV; // 0..0.00390625 regardless of tile position in atlas

    highp vec2 uvCoordOffset = tileXY * singleTileSizeInUV; // where the tile starts in the atlas, using uv coord (0..1)

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


    gl_FragColor = vec4(texture2D(tilesAtlas, finalUVCoordForTile));




	//gl_FragColor = fragInAtlas;
	//gl_FragColor = vec4((gl_FragCoord.xy / vec2(512, 512)), 0, 1.0);

	//vec4 atlascol = texture2D(tilesAtlas, v_texCoords);
	//vec4 tilemapcol = texture2D(tilemap, v_texCoords);

	//gl_FragColor = atlascol * tilemapcol;
	//gl_FragColor = vec4(v_texCoords.x, v_texCoords.y, 0, 1.0);
}