Possible Retina issue with OpenGL ES on iPhone?

Question

This is probably due to another unsolved mystery .

I am drawing Orthographic 2d on an iPhone using a real device and simulator. I am trying to color my pixels of a given color depending on how far they are from an arbitrary point in the pixel space "A" that I am transmitting (hard code). I do everything in Retina resolution 960x640. I calculate the distance from A to gl_FragCoord , and I am the color based on the jump between 2 colors with a maximum distance of 300 pixels.

When on the simulator (with the retina displayed) I need to give the center point “460” pixels for the middle earring of the X screen. YI gives 160 pixels and I look for a distance of 300 feet to get the same effect on the device I need a 960X center and a distance of 150, to get the same results (interestingly, the px 80 does not give the same results that I want, but 160 may be an overshoot of the original ...)

Obviously, the problem of the retina is playing. But where and how, and how to find and fix it?

I use:

glViewport(0, 0, 960.0f, 640.0f);

and

glGetRenderbufferParameteriv(GL_RENDERBUFFER, GL_RENDERBUFFER_WIDTH, &framebufferWidth); glGetRenderbufferParameteriv(GL_RENDERBUFFER, GL_RENDERBUFFER_HEIGHT, &framebufferHeight);

and

[self setView:[[EAGLView alloc] initWithFrame:[UIScreen mainScreen].bounds]];
[(EAGLView *)[self view] setContentScaleFactor:2.0f];

Answer 1

You should not hardcode "glViewport (0, 0, 960.0f, 640.0f);", configure the viewport in this way:

 glViewport(0, 0, framebufferWidth, framebufferHeight); 

Also do not print the scale of the content, you can find out the scale of the content with:

 float contentScale = 1.0f; if ([[UIScreen mainScreen] respondsToSelector:@selector(displayLinkWithTarget:selector:)]) { contentScale = [[UIScreen mainScreen] scale]; } 

About pixel distance, since you want the distance to be double with retina display, you can add uniforms to your shader using the content scale.

Answer 2

IOS devices can now have several different screens, and UIWindow can be placed on a non-main screen. In this case, you can use self.view.window.screen.scale to dynamically scale the screen.