From 6f7d04be21de7bdfce3c7c38a4d5fae17451b409 Mon Sep 17 00:00:00 2001
From: Niklas Haas <git@nand.wakku.to>
Date: Mon, 20 Jul 2015 19:09:22 +0200
Subject: vo_opengl: add temporal-dither-period option

This was requested multiple times by users, and it's not hard to
implement and/or maintain.
---
 DOCS/man/vo.rst      | 5 +++++
 video/out/gl_video.c | 5 ++++-
 video/out/gl_video.h | 1 +
 3 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/DOCS/man/vo.rst b/DOCS/man/vo.rst
index 18a56fe79c..d6d1db60e8 100644
--- a/DOCS/man/vo.rst
+++ b/DOCS/man/vo.rst
@@ -455,6 +455,11 @@ Available video output drivers are:
         Unfortunately, this can lead to flicker on LCD displays, since these
         have a high reaction time.
 
+    ``temporal-dither-period=<1-128>``
+        Determines how often the dithering pattern is updated when
+        ``temporal-dither`` is in use. 1 (the default) will update on every
+        video frame, 2 on every other frame, etc.
+
     ``debug``
         Check for OpenGL errors, i.e. call ``glGetError()``. Also request a
         debug OpenGL context (which does nothing with current graphics drivers
diff --git a/video/out/gl_video.c b/video/out/gl_video.c
index 6aa5d94a75..8f46daa8d6 100644
--- a/video/out/gl_video.c
+++ b/video/out/gl_video.c
@@ -333,6 +333,7 @@ static const struct packed_fmt_entry mp_packed_formats[] = {
 const struct gl_video_opts gl_video_opts_def = {
     .dither_depth = -1,
     .dither_size = 6,
+    .temporal_dither_period = 1,
     .fbo_format = GL_RGBA16,
     .sigmoid_center = 0.75,
     .sigmoid_slope = 6.5,
@@ -350,6 +351,7 @@ const struct gl_video_opts gl_video_opts_def = {
 const struct gl_video_opts gl_video_opts_hq_def = {
     .dither_depth = 0,
     .dither_size = 6,
+    .temporal_dither_period = 1,
     .fbo_format = GL_RGBA16,
     .fancy_downscaling = 1,
     .sigmoid_center = 0.75,
@@ -438,6 +440,7 @@ const struct m_sub_options gl_video_conf = {
                    ({"fruit", 0}, {"ordered", 1}, {"no", -1})),
         OPT_INTRANGE("dither-size-fruit", dither_size, 0, 2, 8),
         OPT_FLAG("temporal-dither", temporal_dither, 0),
+        OPT_INTRANGE("temporal-dither-period", temporal_dither_period, 0, 1, 128),
         OPT_CHOICE("alpha", alpha_mode, 0,
                    ({"no", 0},
                     {"yes", 1},
@@ -1923,7 +1926,7 @@ static void pass_dither(struct gl_video *p)
     GLSLF("vec2 dither_pos = gl_FragCoord.xy / %d;\n", p->dither_size);
 
     if (p->opts.temporal_dither) {
-        int phase = p->frames_rendered % 8u;
+        int phase = (p->frames_rendered / p->opts.temporal_dither_period) % 8u;
         float r = phase * (M_PI / 2); // rotate
         float m = phase < 4 ? 1 : -1; // mirror
 
diff --git a/video/out/gl_video.h b/video/out/gl_video.h
index 840fab211c..0881025a14 100644
--- a/video/out/gl_video.h
+++ b/video/out/gl_video.h
@@ -59,6 +59,7 @@ struct gl_video_opts {
     int dither_algo;
     int dither_size;
     int temporal_dither;
+    int temporal_dither_period;
     int fbo_format;
     int alpha_mode;
     int chroma_location;
-- 
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