GL_TEXTURE_RECTANGLE_ARB

问题

I try to use data raw texture using GL_TEXTURE_RECTANGLE_ARB:

void Display::tex(){

GLubyte Texture[16] =
{    
0,0,0,0, 0xFF,0xFF,0xFF,0xFF,
0xFF,0xFF,0xFF,0xFF, 0,0,0,0
};
GLuint Nom;
glLoadIdentity();//load identity matrix
glTranslatef(0.0f,0.0f,-4.0f);//move forward 4 units

glEnable(GL_DEPTH_TEST);    //Active le depth test
glDisable( GL_CULL_FACE );

glEnable (GL_TEXTURE_RECTANGLE_ARB);

glPixelStorei(GL_UNPACK_ROW_LENGTH, 2);

glPixelStorei(GL_UNPACK_ALIGNMENT, 1);

glGenTextures(1, &Nom);

glBindTexture(GL_TEXTURE_RECTANGLE_ARB, Nom);

glTexParameteri(GL_TEXTURE_RECTANGLE_ARB,

                GL_TEXTURE_MIN_FILTER, GL_LINEAR);

glTexImage2D(GL_TEXTURE_RECTANGLE_ARB, 0, GL_RGBA8, 2, 2,

                0, GL_BGRA_EXT, GL_UNSIGNED_INT_8_8_8_8_REV, Texture);
angle  = 0.01 * glutGet ( GLUT_ELAPSED_TIME );
glRotatef(angle,0,1,1);

glBegin(GL_QUADS);  //Et c'est parti pour le cube !

glTexCoord2i(0,0);glVertex3i(-1,-1,-1);
glTexCoord2i(1,0);glVertex3i(+1,-1,-1);
glTexCoord2i(1,1);glVertex3i(+1,+1,-1);
glTexCoord2i(0,1);glVertex3i(-1,+1,-1);

//1 face

glTexCoord2i(0,0);glVertex3i(-1,-1,+1);
glTexCoord2i(1,0);glVertex3i(+1,-1,+1);
glTexCoord2i(1,1);glVertex3i(+1,+1,+1);
glTexCoord2i(0,1);glVertex3i(-1,+1,+1);

//2 faces

glTexCoord2i(0,0);glVertex3i(+1,-1,-1);
glTexCoord2i(1,0);glVertex3i(+1,-1,+1);
glTexCoord2i(1,1);glVertex3i(+1,+1,+1);
glTexCoord2i(0,1);glVertex3i(+1,+1,-1);

//3 faces

glTexCoord2i(0,0);glVertex3i(-1,-1,-1);
glTexCoord2i(1,0);glVertex3i(-1,-1,+1);
glTexCoord2i(1,1);glVertex3i(-1,+1,+1);
glTexCoord2i(0,1);glVertex3i(-1,+1,-1);

//4 faces

glTexCoord2i(1,0);glVertex3i(-1,+1,-1);
glTexCoord2i(1,1);glVertex3i(+1,+1,-1);
glTexCoord2i(0,1);glVertex3i(+1,+1,+1);
glTexCoord2i(0,0);glVertex3i(-1,+1,+1);

//5 faces

glTexCoord2i(1,0);glVertex3i(-1,-1,+1);
glTexCoord2i(1,1);glVertex3i(+1,-1,+1);
glTexCoord2i(0,1);glVertex3i(+1,-1,-1);
glTexCoord2i(0,0);glVertex3i(-1,-1,-1);

//6 faces
glEnd();

glFlush();
}

The result is not very good :

http://shareimage.ro/images/xdkyd12oty44c0qpuo1b.png

The cube should have all faces with an texture 4 square (2 black and 2 white ) .

I dont know where is the error...

回答1:

GL_ARB_texture_rectangle extension uses dimension-dependent texture coordinates. Use [0..W]x[0..H] range for texture coordinates, instead of normalized coordinates range [0..1]x[0..1].

For example, to draw a full image on a quad;

glTexCoord2f(0, 0);                     glVertex3f(...); // top-left
glTexCoord2f(0, imageHeight);           glVertex3f(...); // bottom-left
glTexCoord2f(imageWidth, imageHeight);  glVertex3f(...); // bottom-right
glTexCoord2f(imageWidth, 0);            glVertex3f(...); // top-right

Note that there are several limitations using GL_ARB_texture_rectangle extension.

1. Mipmap filtering is not supported.
2. Texture border is not supported.
3. GL_REPEAT wrap mode is not supported.
4. Palette texture is not supported.
5. texture coods are addressed by [0..w]x[0..h].

Luckily, OpenGL provides GL_ARB_texture_non_power_of_two extension as well to resolve the above limitations, while it is still supporting NPOT (Non Power Of Two) textures.

The biggest advantages of GL_ARB_texture_non_power_of_two are;

1. GL_ARB_texture_non_power_of_two uses the conventional normalized texture coords, [0..1]x[0..1].

2. It does NOT require an additional texture target token, GL_TEXTURE_RECTANGLE_ARB for glEnable(), glTexImage*D(), glBindTexture(), etc. That is, you can still use GL_TEXTURE_2D as usual for NPOT textures.

回答2:

Using texture rectangles, the texture coordinates are absolute pixel positions. In your case your texture coordinates would be 0,0 2,0 2,2 0,2

回答3:

It's working now, see next:

GLubyte Texture[16] =
{
0,0xFF,0,0xFF, 0xFF,0xFF,0xFF,0xFF,
0xFF,0xFF,0xFF,0xFF, 0,0,0,0
};
GLuint Nom;
glClear( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT );   //Efface le framebuffer et le depthbuffer
glMatrixMode(GL_MODELVIEW);     //Un petit gluLookAt()...
glLoadIdentity();//load identity matrix
glTranslatef(0.0f,0.0f,-4.0f);//move forward 4 units
angle  = 0.1 * glutGet ( GLUT_ELAPSED_TIME );
glRotatef(angle,0,2,2);
glEnable(GL_TEXTURE_2D);
glEnable (GL_TEXTURE_RECTANGLE_ARB);
glPixelStorei(GL_UNPACK_ROW_LENGTH, 2);
glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
glGenTextures(1,&Nom);  //Génère un n° de texture
glBindTexture(GL_TEXTURE_2D,Nom);   //Sélectionne ce n°
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, 4, 4, 0, GL_RGB,GL_UNSIGNED_BYTE, Texture);
glTexParameterf(GL_TEXTURE_RECTANGLE_ARB, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE); // GL_CLAMP_TO_EDGE
glTexParameterf(GL_TEXTURE_RECTANGLE_ARB, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE); // GL_CLAMP_TO_EDGE
glTexParameteri(GL_TEXTURE_RECTANGLE_ARB, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_RECTANGLE_ARB, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
glTexImage2D(GL_TEXTURE_RECTANGLE_ARB, 0, GL_RGBA8, 2, 2, 0, GL_BGRA_EXT, GL_UNSIGNED_INT_8_8_8_8_REV, Texture);
glBegin(GL_QUADS);
glTexCoord2i(0,0);glVertex3i(-1,-1,-1);
glTexCoord2i(2,0);glVertex3i(+1,-1,-1);
glTexCoord2i(2,2);glVertex3i(+1,+1,-1);
glTexCoord2i(0,2);glVertex3i(-1,+1,-1);
//1 face
glTexCoord2i(0,0);glVertex3i(-1,-1,+1);
glTexCoord2i(2,0);glVertex3i(+1,-1,+1);
glTexCoord2i(2,2);glVertex3i(+1,+1,+1);
glTexCoord2i(0,2);glVertex3i(-1,+1,+1);
//2 faces
glTexCoord2i(0,0);glVertex3i(+1,-1,-1);
glTexCoord2i(2,0);glVertex3i(+1,-1,+1);
glTexCoord2i(2,2);glVertex3i(+1,+1,+1);
glTexCoord2i(0,2);glVertex3i(+1,+1,-1);
//3 faces
glTexCoord2i(0,0);glVertex3i(-1,-1,-1);
glTexCoord2i(2,0);glVertex3i(-1,-1,+1);
glTexCoord2i(2,2);glVertex3i(-1,+1,+1);
glTexCoord2i(0,2);glVertex3i(-1,+1,-1);
glEnd();
glDisable(GL_TEXTURE_2D);

来源：https://stackoverflow.com/questions/11361583/gl-texture-rectangle-arb