Textures

OpenGL OpenGL: Advanced Coding
1

Hello

I load textures like this:

QImage b;
		QImage t;
		
		if ( !b.load( "ffont.bmp" ) )
		{
			b = QImage( 16, 16, 32);
			b.fill( Qt::red.rgb() );
		}
		
		t = QGLWidget::convertToGLFormat( b );
		glGenTextures( 1, &texture[0]);
		glBindTexture( GL_TEXTURE_2D, texture[0]);
		glTexImage2D( GL_TEXTURE_2D, 0,3, t.width(), t.height(), 0, GL_RGBA, GL_UNSIGNED_BYTE, t.bits());
		glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR );
		glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR );

I would like to store more than just one Texture in a (1) BMP file (e.g. for fonts) and I just dont know how…

I thought I could just write 32 instead of t.width() and it should give me the first 32 pixels of the bitmap. However its not working so far… Or is there a function like glTexCoord2 to set the width and height of the Texture later?

I use Fedora Core 4 and QT.

Thank you for your help!!!

2

How about uploading the whole large texture as one texture object and use texture coordinates to select which sub texture you wish to use (this is how I do it for texture fonts)? This will be more efficient anyway as it reduces the number of texture binds.

Look up “texture atlases.”

-SirKnight

3

Hi

I tried to do it like this:

     glTexCoord2i(0,0);
			    glVertex2d(0,0);			    
			    glTexCoord2i(1/40,0);
			    glVertex2d(22,0);			    
	    		    glTexCoord2i(1/40,1);
			    glVertex2d(22,32);		
			    glTexCoord2i(0,1);			    
			    glVertex2d(0,32);			    
			    glEnd();

…But it doesnt work. It gives me a very distorted texture. What am i doing wrong?

Thank you for your help!

4

IT WORKS!!!

i have to use float instead of int! :rolleyes:

 

			    glBindTexture(GL_TEXTURE_2D, texture[0]);
			    glBegin(GL_QUADS);
			    glTexCoord2f(0.0f,0.0f);
			    glVertex2f(0.0f,0.0f);			    
			    glTexCoord2f(0.025f,0.0f);
			    glVertex2f(22.0f,0.0f);			    
	    		    glTexCoord2f(0.025f,1.0f);
			    glVertex2f(22.0f,32.0f);		
			    glTexCoord2f(0.0f,1.0f);			    
			    glVertex2f(0.0f,32.0f);			    
			    glEnd();

Thank you!!! :slight_smile:

5

it has nothing to do with ogl, but with c+ :wink: when you divide two integers, then the result is also an integer :wink: when at least one of them is float, then the result is float.

so it would be 1/40.0f or 1.0f/40 or 1.0f/40.0f …

6

Originally posted by madmadmod:
IT WORKS!!!
I’ve been having quite a few of those moments recently, cool huh? :slight_smile:

BTW, Glad it works.

-SirKnight