Opengl View drawing issue

Question

For dimension consideration, I resize the opengl view to 2.0 scale than origin, like this:

NSInteger Dimension = 2;
self.glView = [[WQPaintGLView alloc] initWithFrame:CGRectMake(0, 0, width*Dimension, height*Dimension)];

CGAffineTransform tScale        = CGAffineTransformMakeScale((float)1/Dimension, (float)1/Dimension);
CGAffineTransform tTranslate    = CGAffineTransformTranslate(tScale, -width, -height);

self.glView.transform = tTranslate;

[self.canvasContainerView addSubview:self.glView];

But get a strange issue, see:

I can only draw stuff in the left bottom 1/4 area.

What did I wrong?

Answer 1

The UIView transform and openGL are not very compatible. Also the view resizing after the openGL initialization could be troublesome and in most cases a new render buffer must be created from the view.

Anyway since you scaled the view to have a larger surface you should check for following calls:

• glViewport should define what part of the buffer you are writing at. Usually it is set like (0, 0, viewWidth, viewHeight). In your case it must include the scale as well.
• glOrtho (or glFrustum ) define your coordinate system if used. Those should most likely be the same no matter the view scale.
• Any other matrix usage or scissors that may be defined by the view's frame.

By all means if possible remove the transform on the view and try to find a better solution.