Screen deformation with shaders?

OpenGL Development
#1

I would like to create a shader that just messes with the screen. The problem is, I only know how to move individual pixels from the vertex shader. How might I stretch them?

#2

FBOs

#3

Deformation is just mapping coordinates with a function other than [icode](x1, y1) = (x0, y0)[/icode]

Throw this into ShaderToy with some texture loaded in iChannel0:

void main(void)
{
	vec2 uv = gl_FragCoord.xy / iResolution.xy;
	float distFromCenter = distance(uv, vec2(.5));
	uv *= (sin(iGlobalTime) / 2. + 1.) * distFromCenter;
	gl_FragColor = texture2D(iChannel0, uv);
}

Edit: Another, more “stretchy” example: (adds to UV instead of multiply)

void main(void)
{
	vec2 uv = gl_FragCoord.xy / iResolution.xy;
	uv += distance(uv, vec2(.5)) * (sin(iGlobalTime)/4.+.25);
	gl_FragColor = texture2D(iChannel0, uv);
}
#4

If you use the techniques described here to get the coordinates of the screen, then you can just warp the texture coordinates accordingly.

#5

You got me playing with shadertoy again, but I got one that mimics 3D camera movement:

void main(void)
{
	vec2 uv = gl_FragCoord.xy / iResolution.xy;
	uv += (sin(iGlobalTime)/2.+.5) * dot(uv, vec2(.5));
	gl_FragColor = texture2D(iChannel0, uv);
}

Neat.

Change the multiply to a divide and see what happens.

Just mess around until you find something you like.