Practical Algorithms for 3D Computer Graphics, 2nd Edition

288 7. Real-time 3D: OpenGL

const float d=0.01;

// Assumes gray color, get value

float y1 = (texture2D(Rsf, TexCoord+vec2( 0.0, d)).r);

// above and below sample point.

float y2 = (texture2D(Rsf, TexCoord+vec2( 0.0,-d)).r);

// and to left

float x1 = (texture2D(Rsf, TexCoord+vec2( d, 0.0)).r);

// and right

float x2 = (texture2D(Rsf, TexCoord+vec2(-d, 0.0)).r);

vec3 normDelta=normalize(vec3((y2-y1)*Gradient,

(x1-x2)*Gradient,1.0));

Procedural textu res It is in the area of pro ced u r al textures that the real p ower of

the programmable GPU becomes evident. M or e or less any texture that can be

described algorithmically can be programmed into the GPU and