[FFmpeg-devel] [PATCH 2/3] avfilter/delogo: added circular delogo algorithm description

["Jörg Habenicht via ffmpeg-devel" <ffmpeg-devel@ffmpeg.org>]

Added a description of the elliptic formed delogo algorithm. Placed it
outside the doxygen function comment.

Signed-off-by: Jörg Habenicht <j.habenicht@gmx.de>
---
 libavfilter/vf_delogo.c | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/libavfilter/vf_delogo.c b/libavfilter/vf_delogo.c
index 7641c3b483..ea741e2700 100644
--- a/libavfilter/vf_delogo.c
+++ b/libavfilter/vf_delogo.c
@@ -100,6 +100,30 @@ static void apply_delogo(uint8_t *dst, int dst_linesize,
                          int logo_x, int logo_y, int logo_w, int logo_h,
                          unsigned int band, int show, int direct)
 {
+    /* Round area algorithm description:
+     *
+     * logo_x, logo_y, logo_w and logo_h define the boundaries of the
+     * ellipse. In the ellipse formula x^2 / a^2 + y^2 / b^2 = 1 let
+     * a = logo_w/2, b = logo_h/2 and the center of the ellipse
+     * (0,0) = (logo_x + a, logo_y + b).
+     * Let the picture dimensions (px,py,pw,ph) := function API(x,y,w,h).
+     * A point of the picture is transformed into the ellipse coordinates
+     * by using x = px - (logo_x + a), y = py - (logo_y +b).
+     *
+     * A point is inside the ellipse if x^2 / a^2 + y^2 / b^2 <= 1
+     * <=> (x + logo_x)^2 / (logo_w / 2)^2
+     *     + (y + logo_y)^2 / (logo_h / 2)^2 <= 1
+     * <=> (px - logo_x - a + logo_x)^2 / (logo_w / 2)^2
+     *     + (py - logo_y - b + logo_y)^2 / (logo_h / 2)^2 <= 1
+     * <=> (px - a)^2 / (logo_w / 2)^2
+     *     + (py - b)^2 / (logo_h / 2)^2 <= 1
+     * <=> ((px - a) / (logo_w / 2))^2
+     *     + ((py - b) / (logo_h / 2))^2 <= 1
+     *
+     * px is later defined x, py defined y.
+     * logo_w is later defined logo_w2, logo_h defined logo_h2.
+     */
+
     int x, y;
     uint64_t interp, weightl, weightr, weightt, weightb, weight;
     uint8_t *xdst, *xsrc;
--
2.45.3

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