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[BUG] framebuffer size of a mac

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[BUG] framebuffer size of a mac
« on: November 07, 2020, 13:18:45 »
Hello,

I highly suspect this is a bug, and I also expect it to be a bug with glfw. I have an issue there as well: https://github.com/glfw/glfw/issues/1800

However, doesn't hurt to ask around here as well goes my thinking.


I'm rendering a bunch of stuff to a FBO and when I'm done I'm blitting to the default FB.
This works smooth, except for some mac users. Behavior seems a bit erratic.

The problem is I'm not getting the correct framebuffer size glfwGetFramebufferSize. They are doubled.

glBlitFramebuffer(0, 0, offlineW, offlineH, 0, 0, defaultFBW, defaultFBH, GL_COLOR_BUFFER_BIT, GL_NEAREST);
where defaultFB is the values from glfwGetFramebufferSize.

On my IMac listed as (Retina 4K, 21.5-inch, 2017), the display is stated to be 4096 x2304.

glfwGetVideoModes(glfwGetPrimaryMonitor()) returns resolutions from 640x480 -> 4096x2304

If I launch a windowed window with any resolution, I get the same size framebuffer. The blit is working as expected.

If I launch a full screen window, glfwGetFramebufferSize gives me double the numbers. I.e. window = 4096x2304, FB = 8192x4605, window = 2304x1296, FB = 4096x2304, etc. The result of the blit is that the lower-left quadrant of the offline FBO on covers the whole screen, as expected if the FB size were doubled.

I can solve this by: glfwWindowHint(GLFW_COCOA_RETINA_FRAMEBUFFER, GL11.GL_FALSE);
But this sadly doesn't solve it for some other mac users.

I can also solve it by dividing the returned framebuffer by 2, or divide it by glfwGetWidnowSize, but again it doesn't work on all macs. In fact, it will have the reverse effect on some.

So, I'm thinking, as a layman...

Should glfwGetVideoModes(glfwGetPrimaryMonitor()) really return displaymodes > 2304x1296 for me?
Maybe they should, but I'm still getting too big framebuffers sizes. The x2 factor is consistent on every full screen resolution I'm picking.

I'm also interested if there is a potential workaround. I've tried to figure out how to get the framebuffer myself via opengl, but there doesn't seem to be any method out there.
« Last Edit: November 08, 2020, 15:23:51 by jakethesnake »

Re: [BUG] framebuffer size of a mac
« Reply #1 on: November 15, 2020, 15:39:10 »
Calm down everyone, don't answer all at the same time   8)

After a new mac user had new troubles after a os update, I did some more testing and desperate attempts.

With some further testing, I also noticed that the window size that is half of my retina maximum resolution works perfectly. 2305x1296 creates a FB that's 4608x2592. The bigger and smaller screen resolutions reported by glfGetVideoModes also creates twice the size FB, but they simply don't fit in the window. It's like 2308x1296 is "retina compatible", while the other ones aren't, but still GLFW tells me the framebugger is twice the size of those windows.

Meanwhile, opengl tells me the framebuffer is 4608x2592 on all chosen resolutions except 2304x1296 when I poll scissor and viewport size at init.