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Non-power-of-two Textures Example

BlitzMax Forums/OpenGL Module/Non-power-of-two Textures Example

ghislain(Posted 2008) [#1]
Regarding my topic concerning pixel-perfect images
I figured out how to use non-power-of-two textures. For those who like an example:

Strict

Local c_width:Float = 640
Local c_height:Float = 480
GLGraphics c_width, c_height

Local myExtensions:String = String.FromCString( glGetString( GL_EXTENSIONS ) ).ToLower()

?macos
If myExtensions.find("gl_ext_texture_rectangle") = -1 Then
	RuntimeError "Extension not supported!"
	End
End If
?

glviewport (0,0, c_width, c_height)		' origin of avbl screen + width & height
glmatrixmode (gl_projection)			' modelview, projection or texture matrix
glloadidentity ()						' set 4x4 identity matrix
gluortho2d (0.0,c_width,c_height, 0.0)	' creates a matrix For projecting 2d coordinates
glclear(gl_color_buffer_bit)

glmatrixmode (gl_modelview)
glLoadidentity ()

' Enable non-power-of-two textures
glEnable (gl_TEXTURE_RECTANGLE_EXT)	' <--- !!!

' load a pixmap
Local pmap:TPixmap = LoadPixmap ("mapkansas.bmp")
If pmap.format<>PF_RGBA8888 pmap=pmap.Convert( PF_RGBA8888 ) ' convert to RGBA
Local w:Float = PixmapWidth (pmap)
Local h:Float = PixmapHeight (pmap)

' Create/Assign Texture
' All GL_TEXTURE_2D is replaced by GL_TEXTURE_RECTANGLE_EXT
Local texName:Int
glPixelStorei GL_UNPACK_ALIGNMENT, 1
glGenTextures 1, Varptr texName
glBindTexture gl_texture_rectangle_ext, texName ' <--- !!!
glTexImage2D gl_texture_rectangle_ext, 0, GL_RGBA8, pmap.width, pmap.height, 0, GL_RGBA, GL_UNSIGNED_BYTE, pmap.pixels ' <--- !!!

glBegin (gl_quads)

	' TL
	glTexCoord2f 0.0, 0.0
	glvertex2f 0.0, 0.0
	
	' TR
	glTexCoord2f w, 0.0 ' <--- !!! All TexCoord's are in pixels instead of [0.0 - 1.0]
	glVertex2f w, 0.0
	
	' BR
	glTexCoord2f w, h
	glVertex2f w, h
	
	' BL
	glTexCoord2f 0.0, h
	glVertex2f 0.0, h	
	
glEnd
Flip

WaitKey()
End


ghislain


Retimer(Posted 2008) [#2]
Wow. That's actually really useful to me, thanks.


Dreamora(Posted 2008) [#3]
And how well is it supported? I mean older cards and intel onboard would drastically lose performance if the texture isn't power of two anymore ...
are you sure this removes the power of 2 at all and not just the "square" which is inforced due to the used / targeted configurations of BM? (DX7 and OpenGL 1.2)


ghislain(Posted 2008) [#4]
Well, I'm not sure how well it is supported.
At home I've got the official 'OpenGl Programming Guide v1.2'.
It doesn't mention gl_texture_rectangle_ext.

But it wasn't introduced until OpenGl v1.4 I believe.
The newer documentation does support it.

ghislain


Fetze(Posted 2008) [#5]
Its introduced in 1.4 as extension and officially supported sinde 2.0 as far as I know. Unfortunately that doesn't seem to mean that it is also supported on a wide variety on gfx-cards. I'd go with power-of-two-textures to be safe.