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avfilter/drawbox+drawgrid - add option to prevent overwriting of source pixels

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If the user-supplied color in drawbox and drawgrid filters is non-opaque,
the box & grid painting overwrites the input's pixels (including alpha).
Users typically expect the alpha of the specified color to only act as a key
for compositing on top of the main input.

Added option allows users to select between replacement and composition.
Tested and documented.
This commit is contained in:
Gyan Doshi 2017-12-11 22:35:18 +05:30 committed by Lou Logan
parent 980af9a88c
commit 1c76134fe3
2 changed files with 15 additions and 2 deletions
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10
doc/filters.texi
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@ -7146,6 +7146,11 @@ The expression which sets the thickness of the box edge.
A value of @code{fill} will create a filled box. Default value is @code{3}.
See below for the list of accepted constants.
@item replace
Applicable if the input has alpha. With value @code{1}, the pixels of the painted box
will overwrite the video's color and alpha pixels.
Default is @code{0}, which composites the box onto the input, leaving the video's alpha intact.
@end table
The parameters for @var{x}, @var{y}, @var{w} and @var{h} and @var{t} are expressions containing the
@ -7243,6 +7248,11 @@ video with inverted luma.
The expression which sets the thickness of the grid line. Default value is @code{1}.
See below for the list of accepted constants.
@item replace
Applicable if the input has alpha. With @code{1} the pixels of the painted grid
will overwrite the video's color and alpha pixels.
Default is @code{0}, which composites the grid onto the input, leaving the video's alpha intact.
@end table
The parameters for @var{x}, @var{y}, @var{w} and @var{h} and @var{t} are expressions containing the

7
libavfilter/vf_drawbox.c
View File

@ -80,6 +80,7 @@ typedef struct DrawBoxContext {
char *w_expr, *h_expr; ///< expression for width and height
char *t_expr; ///< expression for thickness
int have_alpha;
int replace;
} DrawBoxContext;
static const int NUM_EXPR_EVALS = 5;
@ -213,7 +214,7 @@ static int filter_frame(AVFilterLink *inlink, AVFrame *frame)
int plane, x, y, xb = s->x, yb = s->y;
unsigned char *row[4];
if (s->have_alpha) {
if (s->have_alpha && s->replace) {
for (y = FFMAX(yb, 0); y < frame->height && y < (yb + s->h); y++) {
row[0] = frame->data[0] + y * frame->linesize[0];
row[3] = frame->data[3] + y * frame->linesize[3];
@ -286,6 +287,7 @@ static const AVOption drawbox_options[] = {
{ "c", "set color of the box", OFFSET(color_str), AV_OPT_TYPE_STRING, { .str = "black" }, CHAR_MIN, CHAR_MAX, FLAGS },
{ "thickness", "set the box thickness", OFFSET(t_expr), AV_OPT_TYPE_STRING, { .str="3" }, CHAR_MIN, CHAR_MAX, FLAGS },
{ "t", "set the box thickness", OFFSET(t_expr), AV_OPT_TYPE_STRING, { .str="3" }, CHAR_MIN, CHAR_MAX, FLAGS },
{ "replace", "replace color & alpha", OFFSET(replace), AV_OPT_TYPE_BOOL, { .i64=0 }, 0, 1, FLAGS },
{ NULL }
};
@ -354,7 +356,7 @@ static int drawgrid_filter_frame(AVFilterLink *inlink, AVFrame *frame)
int plane, x, y;
uint8_t *row[4];
if (drawgrid->have_alpha) {
if (drawgrid->have_alpha && drawgrid->replace) {
for (y = 0; y < frame->height; y++) {
row[0] = frame->data[0] + y * frame->linesize[0];
row[3] = frame->data[3] + y * frame->linesize[3];
@ -418,6 +420,7 @@ static const AVOption drawgrid_options[] = {
{ "c", "set color of the grid", OFFSET(color_str), AV_OPT_TYPE_STRING, { .str = "black" }, CHAR_MIN, CHAR_MAX, FLAGS },
{ "thickness", "set grid line thickness", OFFSET(t_expr), AV_OPT_TYPE_STRING, {.str="1"}, CHAR_MIN, CHAR_MAX, FLAGS },
{ "t", "set grid line thickness", OFFSET(t_expr), AV_OPT_TYPE_STRING, {.str="1"}, CHAR_MIN, CHAR_MAX, FLAGS },
{ "replace", "replace color & alpha", OFFSET(replace), AV_OPT_TYPE_BOOL, { .i64=0 }, 0, 1, FLAGS },
{ NULL }
};