Texture error

OpenGL OpenGL: Basic Coding
1

Hello everyone,

I got an error on displaying texture on a quad in OpenGL.
When I place the fist texture it will work (256x256).
But when I place the second texture (201x81) I see a wrong result on the quad.

Both times I use the code shown below.

You can see the textures and results as attachments.

Thanks in advance,

Dennis

Code used both times:

	GLuint texId;
	glGenTextures(1, &texId);
	glBindTexture(GL_TEXTURE_2D, texId);

	glTexImage2D (GL_TEXTURE_2D, 0, GL_RGB, imageWidth, imageHeight, 0, GL_RGB, GL_UNSIGNED_BYTE, imageData);

	glEnable (GL_TEXTURE_2D);
	glBindTexture(GL_TEXTURE_2D, texId);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
	glColor3f(1.0f, 1.0f, 1.0f);
	glBegin (GL_QUADS);
	glTexCoord2f (0.0, 1.0);
	glVertex3f (-4.0, 3.0, 0.0);

	glTexCoord2f (1.0, 1.0);
	glVertex3f (4.0, 3.0, 0.0);

	glTexCoord2f (1.0, 0.0);
	glVertex3f (4.0, -3.0, 0.0);

	glTexCoord2f (0.0, 0.0);
	glVertex3f (-4.0, -3.0, 0.0);
	glEnd ();
2

When you use the TEXTURE_2D target, the size must be a power of two. Otherwise, can use the TEXTURE_RECTANGLE target for that texture or resize it to fit in a power of two texture.

3

That’s was in old OpenGL.

In GL 2.0 and above, you can create any texture and in any size.

4

Could it be the pixel unpack setting? I think the default is 4 bytes alignment try to change it to 1. So try that


 glPixelStorei(GL_UNPACK_ALIGNMENT,1)
...
5

Now I use the glPixelStorei function the image looks a bit better, but it still does not fit in the corners.

(See in attachment)

6

Can you try with GL_NEAREST for both texture min and mag filter. Also maybe your second texture is in RGBA format.

7

Using GL_NEAREST I’ve already tried and also doesn’t work.
The origional image file is an bmp file (I only use PNG for uploading), and bmp can’t be RGBA.

But I made sure it isn’t RGBA and checked the pixels array.

That could not be the problem.

8

Can you attach the source code of your small program to see what happen?

9

Errrr… I think I already know what the problem is…

The problem was largely in the loading of the bitmap…
(Who I got from an tutorial from the internet)

When I use the code shown below as pixels it will work.

Luckily the other error was hindsight for a part of the “glPixelStorei” function.

So… all thanks for help!

Working code for pixels (c = pixels):

	char* red = new char[3]; red[0]=255; red[1]=0; red[2]=0;
	char* green = new char[3]; green[0]=0; green[1]=255; green[2]=0;
	char* blue = new char[3]; blue[0]=0; blue[1]=0; blue[2]=255;
	char* yellow = new char[3]; yellow[0]=255; yellow[1]=255; yellow[2]=0;
	char* orange = new char[3]; orange[0]=255; orange[1]=128; orange[2]=0;
	char* purple = new char[3]; purple[0]=128; purple[1]=0; purple[2]=128;
	char* c = new char[6*3*3];

	c[0]=orange[0];		c[1]=orange[1];		c[2]=orange[2];
	c[3]=purple[0];		c[4]=purple[1];		c[5]=purple[2];
	c[6]=red[0];		c[7]=red[1];		c[8]=red[2];
	c[9]=green[0];		c[10]=green[1];		c[11]=green[2];
	c[12]=blue[0];		c[13]=blue[1];		c[14]=blue[2];
	c[15]=yellow[0];	c[16]=yellow[1];	c[17]=yellow[2];
	c[18]=purple[0];	c[19]=purple[1];	c[20]=purple[2];
	c[21]=red[0];		c[22]=red[1];		c[23]=red[2];
	c[24]=green[0];		c[25]=green[1];		c[26]=green[2];
	c[27]=blue[0];		c[28]=blue[1];		c[29]=blue[2];
	c[30]=yellow[0];	c[31]=yellow[1];	c[32]=yellow[2];
	c[33]=orange[0];	c[34]=orange[1];	c[35]=orange[2];
	c[36]=red[0];		c[37]=red[1];		c[38]=red[2];
	c[39]=green[0];		c[40]=green[1];		c[41]=green[2];
	c[42]=blue[0];		c[43]=blue[1];		c[44]=blue[2];
	c[45]=yellow[0];	c[46]=yellow[1];	c[47]=yellow[2];
	c[48]=orange[0];	c[49]=orange[1];	c[50]=orange[2];
	c[51]=purple[0];	c[52]=purple[1];	c[53]=purple[2];

	delete red, green, blue, yellow, orange, purple;