matio's picture

Drawing textures not of a power of 2

Hi, I'm trying to render a texture that is not a power of 2 (eg 512, 1026 etc). But it only shows the top corner of the image.

		public void LoadTexture(string filename)
		    if (String.IsNullOrEmpty(filename))
		        throw new ArgumentException(filename);
		    int id = GL.GenTexture();
		    GL.BindTexture(TextureTarget.Texture2D, id);
		    Bitmap bmp = new Bitmap(filename);
			width = bmp.Width;
			height = bmp.Height;
			int w2 = (int)PowerOf2(width);
			int h2 = (int)PowerOf2(height);
			Bitmap bmp2 = new Bitmap(w2, h2);
			Graphics gfx = Graphics.FromImage(bmp2);
			gfx.DrawImage(bmp, new Point(0,0));		
			width_ratio = width/w2;
			height_ratio = 1 - height/h2;
		    BitmapData bmp_data = bmp2.LockBits(new Rectangle(0, 0, bmp.Width, bmp.Height), ImageLockMode.ReadOnly, System.Drawing.Imaging.PixelFormat.Format32bppArgb);
		    GL.TexImage2D(TextureTarget.Texture2D, 0, PixelInternalFormat.Rgba, bmp_data.Width, bmp_data.Height, 0,
		        OpenTK.Graphics.OpenGL.PixelFormat.Bgra, PixelType.UnsignedByte, bmp_data.Scan0);
		    // We haven't uploaded mipmaps, so disable mipmapping (otherwise the texture will not appear).
		    // On newer video cards, we can use GL.GenerateMipmaps() or GL.Ext.GenerateMipmaps() to create
		    // mipmaps automatically. In that case, use TextureMinFilter.LinearMipmapLinear to enable them.
		    GL.TexParameter(TextureTarget.Texture2D, TextureParameterName.TextureMinFilter, (int)TextureMinFilter.Linear);
		    GL.TexParameter(TextureTarget.Texture2D, TextureParameterName.TextureMagFilter, (int)TextureMagFilter.Linear);
		    tex = id;
			GL.BindTexture(TextureTarget.Texture2D, tex.tex);
				GL.Begin (BeginMode.Quads);
//					GL.TexCoord2(0,1); GL.Vertex3 (x, y, z);
//					GL.TexCoord2(1,1); GL.Vertex3 (x+width, y, z);
//		            GL.TexCoord2(1,0); GL.Vertex3 (x+width, y+height, z);
//					GL.TexCoord2(0,0); GL.Vertex3 (x, y+height, z);
					GL.TexCoord2(0,1); GL.Vertex2 (x, y+tex.height);		
					GL.TexCoord2(tex.width_ratio,1); GL.Vertex2 (x+tex.width, y+tex.height);
		            GL.TexCoord2(tex.width_ratio,tex.height_ratio);  GL.Vertex2 (x+tex.width, y);
					GL.TexCoord2(0,tex.height_ratio); GL.Vertex2 (x, y);	
				GL.End ();

This is what it looks like on my screen:

and what the picture should be:


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matio's picture

Oops, the images didn't work, and links aren't showing

the Fiddler's picture

You need to link to the image url, not the html page. :)

Does your video card support non-power of two textures?

matio's picture

I don't think so, which is why I'm getting the next power of 2, creating an image that size and blitting on the original

sgsrules's picture

For testing purposes, does it work with a regular power of 2 texture, ie 512x512? I've got a feeling your texcoords aren't setup correctly.

matio's picture

Thanks for your reply. It does seem to work with a regular texture. I'll have to look into the texcoords being wrong

logixoul's picture

It's probably because you're doing integer division: "width_ratio = width/w2;"
When width<w2, this results in 0. You should do "width_ratio = width/(double)w2;" instead.