Fix px_per_unit scaling while rendering in GLMakie

[ffreyer]

Description

The framebuffer_size optimization from #4485 broke rendering with px_per_unit != 1 for me. For example

f,a,p = scatter(rand(10))
# img = Makie.save("px_per_unit.png", f)
screen = display(f, px_per_unit = 0.5)

results in:

render	saved	render with fix

The current version sets the viewport of the final output to the size of the framebuffer color attachment, which is scaled by px_per_unit. The final output is however sized based on real pixels, so we only draw to half of them like this.

This is not caught by tests because they rely on colorbuffer() which reads the framebuffer color attachment, which the copy-to-screen task does not affect.

Type of change

• Bug fix (non-breaking change which fixes an issue)

Checklist

• Added an entry in CHANGELOG.md (for new features and breaking changes)
• Added or changed relevant sections in the documentation
• Added unit tests for new algorithms, conversion methods, etc.
• Added reference image tests for new plotting functions, recipes, visual options, etc.

[asinghvi17]

I just tried this PR on an M1 Mac and got this error when precompiling GLMakie:

Failed to precompile GLMakie [e9467ef8-e4e7-5192-8a1a-b1aee30e663a] to "/Users/anshul/.julia/compiled/v1.11/GLMakie/jl_J0dVQk".
ERROR: LoadError: InexactError: Int32(Inf32)
Stacktrace:
  [1] Int32
    @ ./float.jl:994 [inlined]
  [2] convert
    @ ./number.jl:7 [inlined]
  [3] cconvert
    @ ./essentials.jl:687 [inlined]
  [4] glViewport(x::Int64, y::Int64, width::Float32, height::Float32)
    @ ModernGL ~/.julia/packages/ModernGL/yNrOu/src/functionloading.jl:64
  [5] (::GLMakie.var"#40#42"{Nothing, GLMakie.GLAbstraction.RenderObject{GLMakie.PostprocessPrerender}})(screen::GLMakie.Screen{GLFW.Window})
    @ GLMakie ~/.julia/dev/Makie/GLMakie/src/postprocessing.jl:296
  [6] render_frame(screen::GLMakie.Screen{GLFW.Window}; resize_buffers::Bool)
    @ GLMakie ~/.julia/dev/Makie/GLMakie/src/rendering.jl:102
  [7] render_frame
    @ ~/.julia/dev/Makie/GLMakie/src/rendering.jl:29 [inlined]
  [8] refreshwindowcb(screen::GLMakie.Screen{GLFW.Window}, window::GLFW.Window)
    @ GLMakie ~/.julia/dev/Makie/GLMakie/src/screen.jl:867
  [9] (::GLMakie.var"#74#75"{GLMakie.Screen{GLFW.Window}})(window::GLFW.Window)
    @ GLMakie ~/.julia/dev/Makie/GLMakie/src/screen.jl:871
 [10] _WindowRefreshCallbackWrapper(window::GLFW.Window)
    @ GLFW ~/.julia/packages/GLFW/wmoTL/src/callback.jl:43
in expression starting at /Users/anshul/.julia/dev/Makie/GLMakie/src/precompiles.jl:15
in expression starting at /Users/anshul/.julia/dev/Makie/GLMakie/src/GLMakie.jl:1
in expression starting at stdin:

[MakieBot]

Benchmark Results

SHA: 6a493473f364b0e588fe79f589a5a715c740d421

Warning

These results are subject to substantial noise because GitHub's CI runs on shared machines that are not ideally suited for benchmarking.

[ffreyer]

fair enough. Changed it to use size(root_scene) which is also used for framebuffers.