ascii_tilemap_one_bit_shader_material.gdshader

shader_type canvas_item;

const lowp uvec2 tilemap_size = uvec2(16);

uniform sampler2D tileset;
uniform lowp uvec2 glyph_size;
uniform lowp uint tile_ids[256];

void fragment() {
	lowp uvec2 tilemap_coord = uvec2(UV * vec2(tilemap_size));
	lowp uint tilemap_index = tilemap_coord.x + tilemap_coord.y * tilemap_size.y;
	// Get tile ID in tileset from tile_ids
	lowp uint tile_id = tile_ids[tilemap_index];
	// Get either white or black from the tileset
	lowp uvec2 tileset_coord = uvec2(tile_id % 16u, uint(float(tile_id) / 16.));
	lowp uvec2 position_within_glyph = uvec2(UV * vec2(tilemap_size) * vec2(glyph_size)) % glyph_size;
	COLOR = texelFetch(tileset, ivec2(tileset_coord * glyph_size + position_within_glyph), 0);
}