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programming hints

OpenGL performance hints

Chapter 5 55

... many more vertices...

glEnd();

than this:

glBegin(GL_TRIANGLES);

glColor3f(1,2,3);

glVertex3f(...);

... many more vertices...

glEnd();

For performance efficiency avoid glMaterial state changes, especially

within a glBegin/glEnd pair.

regular primitive data

If the vertex data that you give to a display list is regular (that is, every

vertex has the same data associated with it), it is possible for the display

list to optimize the primitive much more effectively than if the data is not

regular.

For example if you wanted to give only a single normal for each face in a

GL_TRIANGLES primitive, the most intuitive way to get the best

performance would look like this:

glBegin(GL_TRIANGLES);

glNormal3fv(&v1);

glVertex3fv(&p1); glVertex3fv(&p2); glVertex3fv(&p3);

glNormal3fv(&v2);

glVertex3fv(&p4); glVertex3fv(&p5); glVertex3fv(&p6);

...

glEnd();

In immediate mode, this would give you the best performance. However,

if you are putting these calls into a display list, you will get much better

performance by duplicating the normal for each vertex, thereby giving

regular data to the display list:

glBegin(GL_TRIANGLES);

glNormal3fv(&v1); glVertex3fv(&p1);

glNormal3fv(&v1); glVertex3fv(&p2);

glNormal3fv(&v1); glVertex3fv(&p3);

glNormal3fv(&v2); glVertex3fv(&p4);

OGLImp.book Page 55 Tuesday, February 14, 2006 9:15 AM

HP j6700 Supplementary Guide

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