Hello!
Looking at the OpenGL specification, and then looking at Mesa sources. One
thing is not clear. When using non-compiled vertex arrays the OpenGL 1.1
specification warns you no to change the elements of memory previously
specified glVertexPointer between the glBegin/glEnd pair! But it doesn't
warn you doing it between them.
What the output of the following program should be? In my interpretation of
OGL 1.1 specs it should be a Green rect inside of a black. Or is the output
of the program is undefined?
(Mesa draws to Green).
So I think in glEnd we should check whatever there are array elements used
between the pair and in that case we should translate/or flush them from
glEnd.
Btw. I don't see any reason behind such programs. It could call
glColorPointer again after changing the datas.
#include <GL/glut.h>
/*
** OpenGL Drawing
*/
static void bugg(void)
{
int i;
/* BlackColor*/
float colors[] = {0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0};
/* Clear color buffer to yellow */
glClearColor(1.0f, 1.0f, 0.0f, 1.0f);
glClear(GL_COLOR_BUFFER_BIT);
glEnable(GL_SMOOTH);
glColorPointer(4,GL_FLOAT,0,colors);
glEnableClientState(GL_COLOR_ARRAY);
glBegin(GL_POLYGON);
glArrayElement(1);
glVertex3d( 0.8, 0.8, 0.0);
glArrayElement(1);
glVertex3d( 0.8, -0.8, 0.0);
glArrayElement(1);
glVertex3d(-0.8, -0.8, 0.0);
glArrayElement(1);
glVertex3d(-0.8, 0.8, 0.0);
glEnd();
/* change to green */
colors[0] = 1.0;
colors[5] = 1.0;
glBegin(GL_POLYGON);
glArrayElement(1);
glVertex3d( 0.6, 0.6, 0.0);
glArrayElement(1);
glVertex3d( 0.6, -0.6, 0.0);
glArrayElement(1);
glVertex3d(-0.6, -0.6, 0.0);
glArrayElement(1);
glVertex3d(-0.6, 0.6, 0.0);
glEnd();
/* Ensure completion */
glFinish();
}
/*
** Macintosh main routine
*/
int main(int argc,char **argv)
{
glutInit(&argc,argv);
glutCreateWindow("Hello!");
glutDisplayFunc(bugg);
glutMainLoop();
return 0;
}
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