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compositor: Skip pads that are completely obscured by a higher zorder pad

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For each frame, compare the frame boundaries, check if the format contains an
alpha channel, check opacity, and skip the frame if it's going to be completely
overwritten by a higher zorder frame. The check is O(n^2), but that doesn't
matter here because the number of sinkpads is small.

More can be done to avoid needless drawing, but this covers the majority of
cases. See TODOs. Ideally, a reverse painter's algorithm should be used for
optimal drawing, but memcpy during compositing is small compared to the CPU used
for frame conversion on each pad.

https://bugzilla.gnome.org/show_bug.cgi?id=746147
This commit is contained in:
Nirbheek Chauhan 2015-04-18 15:09:02 +05:30 committed by Tim-Philipp Müller
parent 6fc55a997e
commit e0fd23cb23
1 changed files with 84 additions and 0 deletions
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84
gst/compositor/compositor.c
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@ -296,6 +296,17 @@ gst_compositor_pad_set_info (GstVideoAggregatorPad * pad,
return TRUE;
}
/* Test whether rectangle2 contains rectangle 1 (geometrically) */
static gboolean
is_rectangle_contained (GstVideoRectangle rect1, GstVideoRectangle rect2)
{
if ((rect2.x <= rect1.x) && (rect2.y <= rect1.y) &&
((rect2.x + rect2.w) >= (rect1.x + rect1.w)) &&
((rect2.y + rect2.h) >= (rect1.y + rect1.h)))
return TRUE;
return FALSE;
}
static gboolean
gst_compositor_pad_prepare_frame (GstVideoAggregatorPad * pad,
GstVideoAggregator * vagg)
@ -307,6 +318,11 @@ gst_compositor_pad_prepare_frame (GstVideoAggregatorPad * pad,
GstVideoFrame *frame;
static GstAllocationParams params = { 0, 15, 0, 0, };
gint width, height;
gboolean frame_obscured = FALSE;
GList *l;
/* The rectangle representing this frame, clamped to the video's boundaries.
* Due to the clamping, this is different from the frame width/height above. */
GstVideoRectangle frame_rect;
if (!pad->buffer)
return TRUE;
@ -319,6 +335,17 @@ gst_compositor_pad_prepare_frame (GstVideoAggregatorPad * pad,
return FALSE;
}
/* There's three types of width/height here:
* 1. GST_VIDEO_FRAME_WIDTH/HEIGHT:
* The frame width/height (same as pad->buffer_vinfo.height/width;
* see gst_video_frame_map())
* 2. cpad->width/height:
* The optional pad property for scaling the frame (if zero, the video is
* left unscaled)
* 3. conversion_info.width/height:
* Equal to cpad->width/height if it's set, otherwise it's the frame
* width/height. See ->set_info()
* */
if (cpad->width > 0)
width = cpad->width;
else
@ -394,6 +421,60 @@ gst_compositor_pad_prepare_frame (GstVideoAggregatorPad * pad,
g_free (wanted_colorimetry);
}
/* Clamp the x/y coordinates of this frame to the video boundaries to cover
* the case where (say, with negative xpos/ypos) the non-obscured portion of
* the frame could be outside the bounds of the video itself and hence not
* visible at all */
frame_rect.x = CLAMP (cpad->xpos, 0,
GST_VIDEO_INFO_WIDTH (&pad->buffer_vinfo));
frame_rect.y = CLAMP (cpad->ypos, 0,
GST_VIDEO_INFO_HEIGHT (&pad->buffer_vinfo));
/* Clamp the width/height to the frame boundaries as well */
frame_rect.w = MIN (GST_VIDEO_INFO_WIDTH (&cpad->conversion_info),
GST_VIDEO_INFO_WIDTH (&pad->buffer_vinfo) - cpad->xpos);
frame_rect.h = MIN (GST_VIDEO_INFO_HEIGHT (&cpad->conversion_info),
GST_VIDEO_INFO_HEIGHT (&pad->buffer_vinfo) - cpad->ypos);
GST_OBJECT_LOCK (vagg);
/* Check if this frame is obscured by a higher-zorder frame
* TODO: Also skip a frame if it's obscured by a combination of
* higher-zorder frames */
for (l = g_list_find (GST_ELEMENT (vagg)->sinkpads, pad)->next; l;
l = l->next) {
GstVideoRectangle frame2_rect;
GstVideoAggregatorPad *pad2 = l->data;
GstCompositorPad *cpad2 = GST_COMPOSITOR_PAD (pad2);
/* We don't need to clamp the coords of the second rectangle */
frame2_rect.x = cpad2->xpos;
frame2_rect.y = cpad2->ypos;
/* This is effectively what set_info and the above conversion
* code do to calculate the desired width/height */
frame2_rect.w = cpad2->width ? cpad2->width :
GST_VIDEO_INFO_WIDTH (&cpad2->conversion_info);
frame2_rect.h = cpad2->height ? cpad2->height :
GST_VIDEO_INFO_HEIGHT (&cpad2->conversion_info);
/* Check if there's a buffer to be aggregated, ensure it can't have an alpha
* channel, then check opacity and frame boundaries */
if (pad2->buffer && cpad2->alpha == 1.0 &&
!GST_VIDEO_INFO_HAS_ALPHA (&pad2->info) &&
is_rectangle_contained (frame_rect, frame2_rect)) {
frame_obscured = TRUE;
GST_DEBUG_OBJECT (pad, "Obscured by %s, skipping frame",
GST_PAD_NAME (pad2));
break;
}
}
GST_OBJECT_UNLOCK (vagg);
if (frame_obscured) {
converted_frame = NULL;
gst_video_frame_unmap (frame);
g_slice_free (GstVideoFrame, frame);
goto done;
}
if (cpad->alpha == 0.0) {
GST_DEBUG_OBJECT (vagg, "Pad has alpha 0.0, not converting frame");
converted_frame = NULL;
@ -428,6 +509,7 @@ gst_compositor_pad_prepare_frame (GstVideoAggregatorPad * pad,
converted_frame = frame;
}
done:
pad->aggregated_frame = converted_frame;
return TRUE;
@ -808,6 +890,8 @@ gst_compositor_aggregate_frames (GstVideoAggregator * vagg, GstBuffer * outbuf)
outframe = &out_frame;
/* default to blending */
composite = self->blend;
/* TODO: If the frames to be composited completely obscure the background,
* don't bother drawing the background at all. */
switch (self->background) {
case COMPOSITOR_BACKGROUND_CHECKER:
self->fill_checker (outframe);