Mipmap behaviour: NVidia vs. ATI

[Chris M.]

I have encountered a problem using mipmaps in our software running on
a Ati 9200 Mobility card.
To restrain to the difference i tested mipmaps with the "mipmap.c"
file from the red book. It is the
example where every mipmap level is painted with another color.

I have inserted these too lines to restrict the levels used for
rendering:

glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAX_LOD, 1000.0);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MIN_LOD, 0.0);

including glext.h (hope this isnt the error)

On a GeForce 4 i get the appropriate frame with different mipmap
levels greater than 0.
In contrast the ati mobility card doesnt show anything (just
background color).
If i am changing the parameter GL_TEXTURE_MIN_LOD to -1000 (the
default value) both cards show the same results.

Is the value 0.0 for GL_TEXTURE_MIN_LOD illegal, so that i am doing
something wrong or is there another
reason for the different behaviour ?


Full example of mipmap with the two additional lines:

#include "lib/GL/glut.h"
#include "lib/GL/glext.h"
#include <stdlib.h>

GLubyte mipmapImage32[32][32][4];
GLubyte mipmapImage16[16][16][4];
GLubyte mipmapImage8[8][8][4];
GLubyte mipmapImage4[4][4][4];
GLubyte mipmapImage2[2][2][4];
GLubyte mipmapImage1[1][1][4];

#ifdef GL_VERSION_1_1
static GLuint texName;
#endif

void makeImages(void)
{
int i, j;

for (i = 0; i < 32; i++) {
for (j = 0; j < 32; j++) {
mipmapImage32[j][0] = 255;
mipmapImage32[j][1] = 255;
mipmapImage32[j][2] = 0;
mipmapImage32[j][3] = 255;
}
}
for (i = 0; i < 16; i++) {
for (j = 0; j < 16; j++) {
mipmapImage16[j][0] = 255;
mipmapImage16[j][1] = 0;
mipmapImage16[j][2] = 255;
mipmapImage16[j][3] = 255;
}
}
for (i = 0; i < 8; i++) {
for (j = 0; j < 8; j++) {
mipmapImage8[j][0] = 255;
mipmapImage8[j][1] = 0;
mipmapImage8[j][2] = 0;
mipmapImage8[j][3] = 255;
}
}
for (i = 0; i < 4; i++) {
for (j = 0; j < 4; j++) {
mipmapImage4[j][0] = 0;
mipmapImage4[j][1] = 255;
mipmapImage4[j][2] = 0;
mipmapImage4[j][3] = 255;
}
}
for (i = 0; i < 2; i++) {
for (j = 0; j < 2; j++) {
mipmapImage2[j][0] = 0;
mipmapImage2[j][1] = 0;
mipmapImage2[j][2] = 255;
mipmapImage2[j][3] = 255;
}
}
mipmapImage1[0][0][0] = 255;
mipmapImage1[0][0][1] = 255;
mipmapImage1[0][0][2] = 255;
mipmapImage1[0][0][3] = 255;
}

void init(void)
{
glEnable(GL_DEPTH_TEST);
glShadeModel(GL_FLAT);

glTranslatef(0.0, 0.0, -3.6);
makeImages();
glPixelStorei(GL_UNPACK_ALIGNMENT, 1);

#ifdef GL_VERSION_1_1
glGenTextures(1, &texName);
glBindTexture(GL_TEXTURE_2D, texName);
#endif
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER,
GL_NEAREST_MIPMAP_NEAREST);

glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAX_LOD, 1000.0);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MIN_LOD, 1.0);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, 32, 32, 0,
GL_RGBA, GL_UNSIGNED_BYTE, mipmapImage32);
glTexImage2D(GL_TEXTURE_2D, 1, GL_RGBA, 16, 16, 0,
GL_RGBA, GL_UNSIGNED_BYTE, mipmapImage16);
glTexImage2D(GL_TEXTURE_2D, 2, GL_RGBA, 8, 8, 0,
GL_RGBA, GL_UNSIGNED_BYTE, mipmapImage8);
glTexImage2D(GL_TEXTURE_2D, 3, GL_RGBA, 4, 4, 0,
GL_RGBA, GL_UNSIGNED_BYTE, mipmapImage4);
glTexImage2D(GL_TEXTURE_2D, 4, GL_RGBA, 2, 2, 0,
GL_RGBA, GL_UNSIGNED_BYTE, mipmapImage2);
glTexImage2D(GL_TEXTURE_2D, 5, GL_RGBA, 1, 1, 0,
GL_RGBA, GL_UNSIGNED_BYTE, mipmapImage1);

glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_DECAL);
glEnable(GL_TEXTURE_2D);
}

void display(void)
{
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
#ifdef GL_VERSION_1_1
glBindTexture(GL_TEXTURE_2D, texName);
#endif
glBegin(GL_QUADS);
glTexCoord2f(0.0, 0.0); glVertex3f(-2.0, -1.0, 0.0);
glTexCoord2f(0.0, 8.0); glVertex3f(-2.0, 1.0, 0.0);
glTexCoord2f(8.0, 8.0); glVertex3f(2000.0, 1.0, -6000.0);
glTexCoord2f(8.0, 0.0); glVertex3f(2000.0, -1.0, -6000.0);
glEnd();
glFlush();
}

void reshape(int w, int h)
{
glViewport(0, 0, (GLsizei) w, (GLsizei) h);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluPerspective(60.0, (GLfloat)w/(GLfloat)h, 1.0, 30000.0);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
}

void keyboard (unsigned char key, int x, int y)
{
switch (key) {
case 27:
exit(0);
break;
default:
break;
}
}

int main(int argc, char** argv)
{
glutInit(&argc, argv);
glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB | GLUT_DEPTH);
glutInitWindowSize (500, 500);
glutInitWindowPosition (50, 50);
glutCreateWindow (argv[0]);
init ();
glutDisplayFunc(display);
glutReshapeFunc(reshape);
glutKeyboardFunc(keyboard);
glutMainLoop();
return 0;
}