Pixel Perfect Images - How?

BlitzMax Forums/OpenGL Module/Pixel Perfect Images - How?

ghislain

(Posted 2008) [#1]

Hello,

Is it possible to create pixel perfect images in OpenGL?
What I mean:
- one sets a graphic mode eg: 320,200
- one creates a quad the same size as an image
- one applies a texture [from this image] to the quad

Somehow, I'm unable to create one.
There is always some fuzzyness at the end in my image..

Some code:

Strict

Local c_width:Int = 320
Local c_height:Int = 200
GLGraphics c_width, c_height ', 16

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, c_width, c_height, 0)		' creates a matrix for projecting 2d coordinates
glclear(gl_color_buffer_bit)

glmatrixmode (gl_modelview)
glLoadidentity ()

Local pmap:TPixmap = LoadPixmap ("mapkansas.bmp")
Local texInt:Int = GLTexFromPixmap (pmap, False)
glBindTexture (gl_texture_2d, texInt )
glTexParameteri GL_TEXTURE_2D,GL_TEXTURE_MIN_FILTER,GL_NEAREST
glTexParameteri GL_TEXTURE_2D,GL_TEXTURE_MAG_FILTER,GL_NEAREST
Local w:Float = PixmapWidth (pmap)  - 1
Local h:Float = PixmapHeight (pmap)  - 1

glEnable (gl_texture_2d)

' glTranslatef(0.375, 0.375, 0.0)


glBegin (gl_quads)

' TL
glTexCoord2f 0.0, 0.0
glvertex2f 0.0, 0.0

' TR
glTexCoord2f 1.0, 0.0
glVertex2f w, 0.0

' BR
glTexCoord2f 1.0, 1.0
glVertex2f w, h

' BL
glTexCoord2f 0.0, 1.0
glVertex2f 0.0, h	

glEnd


Flip

WaitKey()
End

It must be possible - Max2d creates them.. But how?

Ghislain

Warpy

(Posted 2008) [#2]

It's something to do with mipmapping and filtering, I think.

ImaginaryHuman

(Posted 2008) [#3]

Not sure but maybe making a quad from 0,0 to 320,240 is slightly too big. Should be from 0,0 to 319,239 (.. converted to float 0..1 range), it'll be 0.9 something ???

ghislain

(Posted 2008) [#4]

I think i solved the problem..

The image size wasn't a power of 2. It seems GLTexFromPixmap creates a texture from the image which is being stretched to the correct texture-size. I expect the artefacts are created during this stretching..

The solution seems to be:
- use images with a correct size, or
- create a texture and copy the pixmap but don't stretch it. instead calculate new texcoords..

ghislain