vo_opengl: always dither

Dithering was disabled if the input bit depth was not larger than the
output bit depth of the screen framebuffer. But since scaling, RGB
conversion, and other filters change the number of significant bits
anyway, dithering could still benefit image quality even in these
cases. Always do dithering, unless dithering is completely disabled.

The original intention of this mechanism was not to change the image
needlessly when playing video that matches the native bit depth of the
screen.

2 files changed, 12 insertions, 30 deletions

diff --git a/DOCS/man/en/vo.rst b/DOCS/man/en/vo.rst
index 824342b279..b87f982632 100644
--- a/DOCS/man/en/vo.rst
+++ b/DOCS/man/en/vo.rst
@@ -337,11 +337,6 @@ opengl
         8
             Dither to 8 bit output.
 
-        Note that dithering will always be disabled if the bit depth
-        of the video is lower or equal to the detected dither-depth.
-        If color management is enabled, input depth is assumed to be
-        16 bits, because the 3D LUT output is 16 bit wide.
-
         Note that the depth of the connected video display device can not be
         detected. Often, LCD panels will do dithering on their own, which
         conflicts with vo_opengl's dithering, and leads to ugly output.
diff --git a/video/out/vo_opengl.c b/video/out/vo_opengl.c
index a44c467b64..cc67187a0f 100644
--- a/video/out/vo_opengl.c
+++ b/video/out/vo_opengl.c
@@ -194,7 +194,6 @@ struct gl_priv {
     // per pixel (full pixel when packed, each component when planar)
     int plane_bytes;
     int plane_bits;
-    int component_bits;
 
     GLint gl_internal_format;
     GLenum gl_format;
@@ -231,20 +230,19 @@ struct fmt_entry {
     int mp_format;
     GLint internal_format;
     GLenum format;
-    int component_bits;
     GLenum type;
 };
 
 static const struct fmt_entry mp_to_gl_formats[] = {
-    {IMGFMT_RGB48,   GL_RGB16, GL_RGB,  16, GL_UNSIGNED_SHORT},
-    {IMGFMT_RGB24,   GL_RGB,   GL_RGB,  8,  GL_UNSIGNED_BYTE},
-    {IMGFMT_RGBA,    GL_RGBA,  GL_RGBA, 8,  GL_UNSIGNED_BYTE},
-    {IMGFMT_RGB15,   GL_RGBA,  GL_RGBA, 5,  GL_UNSIGNED_SHORT_1_5_5_5_REV},
-    {IMGFMT_RGB16,   GL_RGB,   GL_RGB,  6,  GL_UNSIGNED_SHORT_5_6_5_REV},
-    {IMGFMT_BGR15,   GL_RGBA,  GL_BGRA, 5,  GL_UNSIGNED_SHORT_1_5_5_5_REV},
-    {IMGFMT_BGR16,   GL_RGB,   GL_RGB,  6,  GL_UNSIGNED_SHORT_5_6_5},
-    {IMGFMT_BGR24,   GL_RGB,   GL_BGR,  8,  GL_UNSIGNED_BYTE},
-    {IMGFMT_BGRA,    GL_RGBA,  GL_BGRA, 8,  GL_UNSIGNED_BYTE},
+    {IMGFMT_RGB48,   GL_RGB16, GL_RGB,  GL_UNSIGNED_SHORT},
+    {IMGFMT_RGB24,   GL_RGB,   GL_RGB,  GL_UNSIGNED_BYTE},
+    {IMGFMT_RGBA,    GL_RGBA,  GL_RGBA, GL_UNSIGNED_BYTE},
+    {IMGFMT_RGB15,   GL_RGBA,  GL_RGBA, GL_UNSIGNED_SHORT_1_5_5_5_REV},
+    {IMGFMT_RGB16,   GL_RGB,   GL_RGB,  GL_UNSIGNED_SHORT_5_6_5_REV},
+    {IMGFMT_BGR15,   GL_RGBA,  GL_BGRA, GL_UNSIGNED_SHORT_1_5_5_5_REV},
+    {IMGFMT_BGR16,   GL_RGB,   GL_RGB,  GL_UNSIGNED_SHORT_5_6_5},
+    {IMGFMT_BGR24,   GL_RGB,   GL_BGR,  GL_UNSIGNED_BYTE},
+    {IMGFMT_BGRA,    GL_RGBA,  GL_BGRA, GL_UNSIGNED_BYTE},
     {0},
 };
 
@@ -885,14 +883,10 @@ static void init_dither(struct gl_priv *p)
     if (p->dither_depth > 0)
         dst_depth = p->dither_depth;
 
-    int src_depth = p->component_bits;
-    if (p->use_lut_3d)
-        src_depth = 16;
-
-    if (dst_depth >= src_depth || p->dither_depth < 0 || src_depth < 0)
+    if (p->dither_depth < 0)
         return;
 
-    mp_msg(MSGT_VO, MSGL_V, "[gl] Dither %d->%d.\n", src_depth, dst_depth);
+    mp_msg(MSGT_VO, MSGL_V, "[gl] Dither to %d.\n", dst_depth);
 
     // This defines how many bits are considered significant for output on
     // screen. The superfluous bits will be used for rounded according to the
@@ -1562,7 +1556,6 @@ static bool init_format(int fmt, struct gl_priv *init)
         return false;
 
     init->image_format = fmt;
-    init->component_bits = -1;
     init->plane_bits = desc.plane_bits;
 
     // RGB/packed formats
@@ -1572,7 +1565,6 @@ static bool init_format(int fmt, struct gl_priv *init)
             init->plane_bits = desc.bpp[0];
             init->gl_format = e->format;
             init->gl_internal_format = e->internal_format;
-            init->component_bits = e->component_bits;
             init->gl_type = e->type;
             break;
         }
@@ -1581,7 +1573,6 @@ static bool init_format(int fmt, struct gl_priv *init)
     // YUV/planar formats
     if (!supported && (desc.flags & MP_IMGFLAG_YUV_P)) {
         init->gl_format = GL_RED;
-        init->component_bits = init->plane_bits;
         if (init->plane_bits == 8) {
             supported = true;
             init->gl_internal_format = GL_RED;
@@ -1596,7 +1587,7 @@ static bool init_format(int fmt, struct gl_priv *init)
     // RGB/planar
     if (!supported && fmt == IMGFMT_GBRP) {
         supported = true;
-        init->plane_bits = init->component_bits = 8;
+        init->plane_bits = 8;
         init->gl_format = GL_RED;
         init->gl_internal_format = GL_RED;
         init->gl_type = GL_UNSIGNED_BYTE;
@@ -2290,10 +2281,6 @@ static const char help_text[] =
 "        8 bits per component are assumed.\n"
 "     8: Dither to 8 bit output.\n"
 "    Default: -1.\n"
-"    Note that dithering will always be disabled if the bit depth\n"
-"    of the video is lower or qual to the detected dither-depth.\n"
-"    If color management is enabled, input depth is assumed to be\n"
-"    16 bits, because the 3D LUT output is 16 bit wide.\n"
 "  debug\n"
 "    Check for OpenGL errors, i.e. call glGetError(). Also request a\n"
 "    debug OpenGL context.\n"