// brick example fragment shader

// shader constants, could be passed in to allow modification
float width=.25, height = .1, mortar = .01;
vec4 brick_color = vec4(1.,0.,0.,1.);
vec4 mortar_color = vec4(.5,.5,.5,1.);

void
main()
{
    // find row and column for this pixel
    float bs = gl_TexCoord[0].x, bt = gl_TexCoord[0].y;

    // offset even rows by half a bt
    if (mod(bt,2.*height)<height) bs += width*.5;

    // wrap texture coordinates to get "brick coordinates"
    bs = mod(bs,width); bt = mod(bt,height);

    // pick color for this pixel, brick or mortar
    if (bt < mortar || bs < mortar)
	gl_FragColor = mortar_color;
    else
	gl_FragColor = brick_color;

    gl_FragColor *= gl_Color;
}