Distance fields for font rendering (Part 1)

Pushing myself forward again, I will publish some entries about implementing font rendering into a texture atlas, encoded with distance fields and with support for Unicode chars (the possibility to reduce the texture size will probably allow large amounts of glyphs in one single texture) to finally show proper labels and text boxes in Engendro3D.


 

By checking info about how to render fonts in OpenGL, I found this question, which lead me to the Valve’s paper (.pdf).

The results, along with the need to have huge amounts of chars pre-rendered to a font atlas for certain languages, got my interest.

Since the Distance fields looks slightly like blurred images, I made a quick png texture in Gimp containing 6 letters (with Eufm10 font) and I used the Gaussian Blur filter (10 radius) to produce this faked distance Field:

wtx_blured

Then, with a very simple GLSL fragment shader, this is the result:

dfblured

No Bilinear interpolation:

gblured_noint

Zoomed into the ‘B’:

zoomblur

No Bilinear interpolation:

zoomblur_noint

Has outline and glow and, while the result is not the best, the logic works.

The shader I wrote can probably be improved a lot, but I will use the same for all the tests I’ll do:

#version 110

uniform float time;
uniform sampler2D tex;

void main()
{
float color = texture2D(tex,gl_TexCoord[0].st).r;
	if (color <= 0.5)
		gl_FragColor = vec4(0,0,1,1);
	else
		if (color <= 0.6){
			gl_FragColor = vec4(1,1,1,1);}
		else
		{
			if (color < 1.0)
				gl_FragColor = max(0.0,1.0 - color) * 
				vec4(.9,.4,.2,1) * 2.0 * max(sin(-time),sin(time));
			else
				gl_FragColor = vec4(0.0);
		}
}

 

In the next part I will show a Distance Field generator in Python and Pillow (PIL).