We now collect this information during node
construction, so use it here.
The concrete change here is that we now avoid
offscreens for container nodes with multiple children,
as long as they don't overlap. In particular, this
avoid offscreens for ellipsized dim labels.
This fixes two issues with the offscreen rendering code for nodes with
bounds not aligned with the pixel grid:
1.) When drawing to an offscreen buffer the size of the offscreen buffer
was rounded up, but then later when used as texture the vertices
correspond to the original bounds with the unrounded size. This could
then result in the offscreen texture being drawn onscreen at a slightly
smaller size, which then lead to it being visually shifted and blurry.
This is fixed by adjusting the u/v coordinates to ignore the padding
region in the offscreen texture that got added by the size increase from
rounding.
2.) The viewport used when rendering to the offscreen buffer was not
aligned with the pixel grid for nodes at coordinates not aligned with
the pixel grid. Then because the content of the offscreen buffer is not
aligned with the pixel grid and later when used as textures sampling
from it will result in interpolated values for an onscreen pixel. This
could also result in shifting and blurriness, especially for nested
offscreen rendering at different offsets.
This is fixed by adding similar padding at the beginning of the
texture and also adjusting the u/v coordinates to ignore this region.
Fixes: https://gitlab.gnome.org/GNOME/gtk/-/issues/3833
There are situations where our "default framebuffer" is not actually
zero, yet we still want to apply a scissor rect.
Generally, 0 is the default framebuffer. But on platforms where we need
to bind a platform-specific feature to a GL_FRAMEBUFFER, we might have a
default that is not 0. For example, on macOS we bind an IOSurfaceRef to
a GL_TEXTURE_RECTANGLE which then is assigned as the backing store for a
framebuffer. This is different than using gsk_gl_renderer_render_texture()
in that we don't want to incur an extra copy to the destination surface
nor do we even have a way to pass a texture_id into render_texture().
If the rendering operation is over an opaque region, we can potentially
avoid clearing a large section of the framebuffer destination. Some cases
you do want to clear, such as when clearing the whole contents as some
drivers have fast paths for that to avoid bringing data back into the
framebuffer.
