/* Viewport width and height */
uniform ivec2 viewport_size;
/* Position of lower left corner of glyph */
uniform ivec2 position;

/* Vertex coordinates: x, y, s, t */
attribute vec4 coords;

/* Output texture coordinate: s, t */
varying vec2 texture_coord_v;

/**
 * Map coordinates such that:
 * (0 .. viewport_size.[xy]) => (-1.0 .. 1.0)
 */
vec2 map_to_screen(vec2 position)
{
    return 2.0 * position / viewport_size - 1.0;
}

void main(void)
{
    gl_Position = vec4(map_to_screen((vec2)position + coords.xy), 0, 1);
    texture_coord_v = coords.zw;
}