With Dear ImGui + software renderer, it draws:
- by default at 250 fps
- drops to 70 fps if you show the color picker
- drops to 10 fps if put the color picker fullscreen
The Renderer logical scaling code scales mouse coordinates, and needs to
take the window DPI into account on HIGHDPI windows. However, the
variable which tracks this, renderer->dpi_scale, is set once when the
renderer is created, and then not updated. In the event that the window
is moved to another screen, or the screen DPI otherwise changes, this
will be outdates, and potentially the coordinates will be all wrong.
So let's update the dpi_scale on the SIZE_CHANGED event: it's at least a
possibility that this will be issued on some OSes when DPI changes, and
it's otherwise already handled by SDL_Renderer's event filter.
The RenderDrawLinesWithRects and RenderDrawLinesWithRectsF functions can
sometimes call QueueCmdFillRects() with the data pointed to by frects
uninitialised. This can occur if none of the lines can be replaced with
rects, in which case the frects array is empty, and nrects is 0.
gcc 10.3.0 will detect this possibility, and print a warning like:
/home/david/Development/SDL/src/render/SDL_render.c: In function 'RenderDrawLinesWithRectsF':
/home/david/Development/SDL/src/render/SDL_render.c:2725:15: warning: '<unknown>' may be used uninitialized [-Wmaybe-uninitialized]
2725 | retval += QueueCmdFillRects(renderer, frects, nrects);
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/home/david/Development/SDL/src/render/SDL_render.c:499:1: note: by argument 2 of type 'const SDL_FRect *' to 'QueueCmdFillRects' declared here
499 | QueueCmdFillRects(SDL_Renderer *renderer, const SDL_FRect * rects, const int count)
| ^~~~~~~~~~~~~~~~~
This is harmless, because when this is uninitialised, nrects is always
0, so QueueCmdFillRects() does nothing anyway. We therefore can work
around this by only calling QueueCmdFillRects() when nrects is nonzero.
Somewhat impressively, gcc recognises that this is now safe.
We now handle HiDPI correctly, and touches are clamped to the viewport. So
if you are rendering to a logical 640x480 in a 720p window, and touch the
letterboxing at point (640,700), it will report the touch at (0.5,1.0) instead
of outside the documented range.
From hmk:
"When scaling is enabled (e.g. via SDL_RenderSetLogicalSize, size not equal
to window size), mouse motion events are also scaled. Small motions are
rounded up (SDL_max() when the value after scaling is less than 1), while
larger motions are truncated by the floating point -> integer conversion.
https://hg.libsdl.org/SDL/file/b18197f9bf9d/src/render/SDL_render.c#l658
The end result feels something like mouse reverse mouse acceleration + angle
snapping at low speeds, but less consistent (amount of truncation & rounding
depends on how fast the mouse is moved) and potentially much worse if the
scaling factor is large. This pretty much makes it useless for anything
where you need precise mouse aiming (think of games). I suspect this is why
aiming gets so terrible in some games that let you use scaling to reduce the
render resolution (e.g. Ion Fury).
With 4x4 scaling, I can reproduce a situation where it takes three fast flicks
of the mouse across the pad to undo one slow sweep across the pad. In other
words, extreme reverse acceleration. This does not happen when scaling is
disabled.
Furthermore, any game that uses relative mouse motion events for 3D camera
rotation probably wants the raw mouse deltas and not a value that depends on
scaling and resolution and rounding and truncation. Ideal camera rotation
just takes mouse input, multiplies it by sensitivity, and adds it to the
angle-in-radians or whatever measure is used for yaw & pitch. Pixels and
screen resolution or window dimensions should not be a part of the equation
at all, even if it could be implemented without rounding errors.
[...]
This [patch] completely eliminates angle snapping for me, and makes
sensitivity consistent. In other words, it's completely usable for, say,
aiming in a first person shooter."
Partially fixes Bugzilla #4811.
Sylvain
Ozkan Sezer
Sam Lantinga
David Gow
Ivan Epifanov
Ryan C. Gordon
Vanfanel
hmk