OpenGL Insights

252 III Bending the Pipeline

in vec3 position [];

out vec4 color ;

void main () {

gl_Position = vec4 ( -0.5 ,0.0 ,0.0 ,1.0);

color = vec4 (+ position [0] ,1.0);

EmitVertex();

gl_Position = vec4 (+0.5 ,0.0 ,0.0 ,1.0);

color = vec4(-position [0] ,1.0);

EmitVertex();

}

Listing 18.2. Bounding-box update geometry shader.

•

Read back the bounding box texture in a buffer attached to the GL PIXEL

PACK BUFFER target.

The vertex shader just passes the local vertex position to the geometry stage. This

position is set as a color of the first pixel by the geometry shader, while the negated

position is written to the second pixel color (see Listing 18.2). We negate the position ...