Syncing task from Mir.
** Changed in: mir (Ubuntu)
Importance: Undecided => Medium
** Changed in: mir (Ubuntu)
Status: New => Triaged
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https://bugs.launchpad.net/bugs/1288021
Title:
MirResizeEvent's width/height fields are not in sync with the next
buffer the client receives
Status in Mir:
Triaged
Status in mir package in Ubuntu:
Triaged
Bug description:
MirResizeEvent's width/height fields are not in sync with the next
buffer the client receives.
This is because they represent the latest dimensions of a surface.
However, due to compositing and frame scheduling, MirResizeEvent
arrives a significant time before the client gets any buffers with the
new dimensions. So if the client actually tries to use the
width/height provided in MirResizeEvent, it will render incorrectly
with ugly artefacts.
Clients should always be using the latest _buffer_ dimensions, and not
the latest surface dimensions. As demonstrated in examples/* the
latest buffer dimensions are available via:
mir_buffer_usage_software: Use the width/height returned by
mir_surface_get_graphics_region().
mir_buffer_usage_hardware: Use the actual buffer dimensions as
accurately reported by EGL as soon as you get a new buffer from
eglSwapBuffers:
eglSwapBuffers(egldisplay, eglsurface);
if (eglQuerySurface(egldisplay, eglsurface, EGL_WIDTH, &width) &&
eglQuerySurface(egldisplay, eglsurface, EGL_HEIGHT, &height))
{
glViewport(0, 0, width, height);
}
This is current best practice, and will result in smooth client
resizing. Unfortunately it means the width/height fields in the
MirResizeEvent structure should be ignored. Perhaps we need to
deprecate them, or perhaps we should enhance them to represent buffer
dimensions instead...
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