terminal emulator shader (for love2d)

file.c

const vec3 WHITE = vec3(1.0);
const vec3 BLACK = vec3(0.0);

uniform vec2 grid_size = vec2(80.0, 50.0);  // size of the terminal grid

uniform vec2 tileset_size = vec2(16.0, 16.0);  // size of the font image or tileset image
uniform float cw = 20.0;  // cell width 
uniform float ch = 20.0;  // cell height

uniform Image tileset;  // the bitmap font image or tileset image

uniform Image bg_tex;   // background grid colors (textures with the same size as the grid (e.g. 80x50))
uniform Image fg_tex;   // foreground grid colors 
uniform Image chr_tex;  // glyph values in the red channel 

vec4 effect(vec4 color, Image TEXTURE, vec2 UV, vec2 SCREEN_UV) {
	vec4 COLOR = color;

	// get tileset size in pixels
	vec2 ts_img_size = vec2(tileset_size.x*cw, tileset_size.y*ch);
	vec2 canvas_size = vec2(grid_size.x*cw, grid_size.y*ch);

	// get the glyph value (stored in the red channel), and scale it to 0-255
	float g = Texel(chr_tex, UV).r * 255.0;

	// get the glyph uv coords on the tileset, in pixels (normalized)
	vec2 guv = vec2(
		floor(mod(g, 16.0))  / ts_img_size.x * cw,
		floor(g/16.0)        / ts_img_size.y * ch
	);

	// Get the pixel offset from the UV, to add to the 'guv' (the glyph's uv coords).
	// (For each cell there's a 'cw*ch' amount of pixels. This determines which pixel
	// we're at in the current cell.)
	vec2 ofs = vec2(
		mod(UV.x*canvas_size.x, cw)   / ts_img_size.x,
		mod(UV.y*canvas_size.y, ch)   / ts_img_size.y
	);

	// Get the color at the glyph's coords IN THE TILESET, offset to the current pixel in the tile
	vec4 px_col = Texel(tileset, guv+ofs);

	// If 'px_col' is white, that means this pixel belongs to the glyph,
	// otherwise this pixel is from the space around the glyph.
	// If white, use fg color, else use bg color

	COLOR = px_col.rgb != BLACK    // I actually inverted this check, because my terminal ensures all fonts have a black background 
		  ? Texel(fg_tex, UV)  // before using them. You could switch this around to check for WHITE pixels instead, if the 
		  : Texel(bg_tex, UV); // terminal supports font images with arbitrary non-black backgrounds (transparent, pink, etc).

	return COLOR;
}