OpenGL Insights

102 IDiscovering

layout (quads) in;

in vec3 tcPosition[];

patch in mat4 cx , cy, cz ;

uniform mat4 Projection;

uniform mat4 Modelview;

void main ()

{

float u=gl_TessCoord.x, v = gl_TessCoord.y;

vec4 U=vec4(u*u*u,u*u,u,1);

vec4 V=vec4(v*v*v,v*v,v,1);

float x=dot(cx * V, U);

float y=dot(cy * V, U);

float z=dot(cz * V, U);

gl_Position = Projection * Modelview * vec4(x , y, z , 1);

}

Listing 6.6. Evaluation shader.

Current drivers have trouble with varying arrays of matrices; we had to replace

the c[] array with three separate matrices.

Further gains could be achieved by removing the for loop and using the barrier

instruction, but current drivers do not support the ...