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(3DS) Fix screen tearing when running 50Hz content

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This commit is contained in:
jdgleaver 2019-04-16 15:41:55 +01:00
parent be7356ec6d
commit a9a5782cc0
1 changed files with 43 additions and 1 deletions
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44
gfx/drivers/ctr_gfx.c
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@ -579,7 +579,49 @@ static bool ctr_frame(void* data, const void* frame,
}
#endif
if (ctr->vsync)
gspWaitForEvent(GSPGPU_EVENT_VBlank0, false);
{
/* If we are running at the display refresh rate,
* then all is well - just wait on the *current* VBlank0
* event and carry on.
*
* If we are running at below the display refresh rate,
* then we have problems: frame updates will happen
* entirely out of sync with VBlank0 events. To elaborate,
* we'll wait for a VBlank0 here, but it will already have
* happened partway through the previous frame. So it's:
* 'oh good - let's render the current frame', but the next
* VBlank0 will occur in less time than it takes to draw the
* current frame, resulting in 'overlap' and screen tearing.
*
* This seems to be a consequence of using the GPU directly.
* Other 3DS homebrew typically uses the ctrulib function
* gfxSwapBuffers(), which ensures an immediate buffer
* swap every time, and no tearing. We can't do this:
* instead, we use a variant of the ctrulib function
* gfxSwapBuffersGpu(), which seems to send a notification,
* and the swap happens when it happens...
*
* I don't know how to fix this 'properly' (probably needs
* some low level rewriting, maybe switching to an implementation
* based on citro3d), but I can at least implement a hack/workaround
* that allows 50Hz content to be run without tearing. This involves
* the following:
*
* If content frame rate is more than 10% lower than the 3DS
* display refresh rate, don't wait on the *current* VBlank0
* event (because it is 'tainted'), but instead wait on the
* *next* VBlank0 event (which will ensure we have enough time
* to write/flush the display buffers).
*
* This fixes screen tearing, but it has a significant impact on
* performance...
* */
bool next_event = false;
struct retro_system_av_info *av_info = video_viewport_get_system_av_info();
if (av_info)
next_event = av_info->timing.fps < video_info->refresh_rate * 0.9f;
gspWaitForEvent(GSPGPU_EVENT_VBlank0, next_event);
}
ctr->vsync_event_pending = true;