Whenever we got a glColor, glNormal, glTexCoord, etc. call outside a
glBegin/End pair, we'd immediately map a vertex buffer to begin
accumulating vertex data. In some cases, such as with display lists,
this led to excessive vertex buffer mapping. For example, if we have
a display list such as:
glNewList(42, GL_COMPILE);
glBegin(prim);
glVertex2f();
...
glVertex2f();
glEnd();
glEndList();
Then did:
glColor3f();
glCallList(42);
We'd map a vertex buffer as soon as we saw glColor3f but we'd never
actually write anything to it. Note that the vertex position data
was put into a vertex buffer during display list compilation.
With this change, we delay mapping the vertex buffer until we actually
have a vertex to write to it (triggered by a glVertex() call). In the
above case, we no longer map a vertex buffer when setting the color and
calling the list.
For drivers such as VMware's, reducing buffer mappings gives improved
performance.
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Brian Paul
f6d4e20d10