topic Re: GMA950 glShadeModel(GL_FLAT) bug in Developing Games on Intel Graphics

GMA950 glShadeModel(GL_FLAT) bug

thegeleto — Sun, 19 Jul 2009 13:10:02 GMT

I've stumbled on a driver bug, where when using glShadeModel(GL_FLAT) the triangle color is not always taken from the last vertex as it should.

Here's how this looks with the Intel card:

... and the same thing with ATI and NVidia cards:

Executable (requires glut32.dll):

Source:

[cpp]#include "stdafx.h"
#include 

void display(void)
{
	int colors[7] = { 0xff0000,0x00ff00,0x0000ff, 0xff00ff,0xff00ff,0xff00ff,0xff00ff };
	int indexes[18] = { 1,2,0,  2,3,0, 0,4,1, 4,5,1, 1,5,2, 5,6,2 };
	float verts[21] = { 0,-2,0, 0,0,0, -1,1,0, -1,-1,0, 1,-1,0, 1,1,0, 0,2,0 };

	glClear( GL_COLOR_BUFFER_BIT );

	glEnableClientState( GL_VERTEX_ARRAY );
	glEnableClientState( GL_COLOR_ARRAY );

	glColorPointer( 4, GL_UNSIGNED_BYTE, 0, colors );
	glVertexPointer( 3, GL_FLOAT, 0, verts );
	glDrawElements( GL_TRIANGLES, 18, GL_UNSIGNED_INT, indexes );

	glDisableClientState( GL_VERTEX_ARRAY );
	glDisableClientState( GL_COLOR_ARRAY );
	
	glFlush();
}

void init(void)
{
	glShadeModel( GL_FLAT );
	glMatrixMode( GL_PROJECTION );
	glLoadIdentity();
	glOrtho( -2, 2, -3, 3, -1, 1 );
}

int _tmain( int argc, char** argv )
{
	glutInit( &argc, argv );
	glutInitDisplayMode( GLUT_SINGLE | GLUT_RGB );
	glutInitWindowSize( 250, 250 );
	glutInitWindowPosition( 100, 100 );
	glutCreateWindow( "Fix me!!!" );
	init();
	glutDisplayFunc( display );
	glutMainLoop();
	return 0;
}[/cpp]

The same thing happens with normals and when using VBO.
Tested on an Asus eeepc 1000h, Windows XP, with drivers version 6.14.10.4906(the latest from Asus) and 6.14.10.4926
BTW, the VBOs on 4926 are very unstable. 4906 has no VBOs

Re: GMA950 glShadeModel(GL_FLAT) bug

Chuck_De_Sylva — Mon, 20 Jul 2009 17:23:58 GMT

Quoting - thegeleto

[cpp]#include "stdafx.h"
#include 

void display(void)
{
	int colors[7] = { 0xff0000,0x00ff00,0x0000ff, 0xff00ff,0xff00ff,0xff00ff,0xff00ff };
	int indexes[18] = { 1,2,0,  2,3,0, 0,4,1, 4,5,1, 1,5,2, 5,6,2 };
	float verts[21] = { 0,-2,0, 0,0,0, -1,1,0, -1,-1,0, 1,-1,0, 1,1,0, 0,2,0 };

	glClear( GL_COLOR_BUFFER_BIT );

	glEnableClientState( GL_VERTEX_ARRAY );
	glEnableClientState( GL_COLOR_ARRAY );

	glColorPointer( 4, GL_UNSIGNED_BYTE, 0, colors );
	glVertexPointer( 3, GL_FLOAT, 0, verts );
	glDrawElements( GL_TRIANGLES, 18, GL_UNSIGNED_INT, indexes );

	glDisableClientState( GL_VERTEX_ARRAY );
	glDisableClientState( GL_COLOR_ARRAY );
	
	glFlush();
}

void init(void)
{
	glShadeModel( GL_FLAT );
	glMatrixMode( GL_PROJECTION );
	glLoadIdentity();
	glOrtho( -2, 2, -3, 3, -1, 1 );
}

int _tmain( int argc, char** argv )
{
	glutInit( &argc, argv );
	glutInitDisplayMode( GLUT_SINGLE | GLUT_RGB );
	glutInitWindowSize( 250, 250 );
	glutInitWindowPosition( 100, 100 );
	glutCreateWindow( "Fix me!!!" );
	init();
	glutDisplayFunc( display );
	glutMainLoop();
	return 0;
}[/cpp]

I will open a driver bug for this. Stay tuned.

Re: GMA950 glShadeModel(GL_FLAT) bug

delle — Sat, 15 May 2010 06:33:02 GMT

>>>I will open a driver bug for this. Stay tuned.

Any news for this?

Re: GMA950 glShadeModel(GL_FLAT) bug

Doraisamy_G_Intel — Tue, 18 May 2010 18:12:12 GMT

Unfortunately, GMA950 is not actively supported anymore. I will check with the team to see if this resolved previously.

Thanks,
-Ganesh