Drawing only part of a texture OpenGL ES iPhone

Posted by Ben Reeves on Stack Overflow See other posts from Stack Overflow or by Ben Reeves
Published on 2010-06-11T12:47:26Z Indexed on 2010/06/11 13:33 UTC
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..Continued on from my previous question

I have a 320*480 RGB565 framebuffer which I wish to draw using OpenGL ES 1.0 on the iPhone.

- (void)setupView
{   
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);

    glTexParameteriv(GL_TEXTURE_2D, GL_TEXTURE_CROP_RECT_OES, (int[4]){0, 0, 480, 320});

    glEnable(GL_TEXTURE_2D);
}

// Updates the OpenGL view when the timer fires
- (void)drawView
{
  // Make sure that you are drawing to the current context 
  [EAGLContext setCurrentContext:context];

  //Get the 320*480 buffer
  const int8_t * frameBuf = [source getNextBuffer];

  //Create enough storage for a 512x512 power of 2 texture
  int8_t lBuf[2*512*512];

  memcpy (lBuf, frameBuf, 320*480*2);

  //Upload the texture
  glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, 512, 512, 0, GL_RGB, GL_UNSIGNED_SHORT_5_6_5, lBuf);

  //Draw it
  glDrawTexiOES(0, 0, 1, 480, 320);

  [context presentRenderbuffer:GL_RENDERBUFFER_OES];
}

If I produce the original texture in 512*512 the output is cropped incorrectly but other than that looks fine. However using the require output size of 320*480 everything is distorted and messed up.

I'm pretty sure it's the way I'm copying the framebuffer into the new 512*512 buffer. I have tried this routine

int8_t lBuf[512][512][2];
const char * frameDataP = frameData;
for (int ii = 0; ii < 480; ++ii) {
    memcpy(lBuf[ii], frameDataP, 320);
    frameDataP += 320;
}

Which is better, but the width appears to be stretched and the height is messed up.

Any help appreciated.

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