gl_video: improve dithering

Use a different algorithm to generate the dithering matrix. This
looks much better than the previous ordered dither matrix with its
cross-hatch artifacts.

The matrix generation algorithm as well as its implementation was
contributed by Wessel Dankers aka Fruit. The code in dither.c is
his implementation, reformatted and with static global variables
removed by me.

The new matrix is uploaded as float texture - before this commit, it
was a normal integer fixed point matrix. This means dithering will
be disabled on systems without float textures.

The size of the dithering matrix can be configured, as the matrix is
generated at runtime. The generation of the matrix can take rather
long, and is already unacceptable with size 8. The default is at 6,
which takes about 100 ms on a Core2 Duo system with dither.c compiled
at -O2, which I consider just about acceptable.

The old ordered dithering is still available and can be selected by
putting the dither=ordered sub-option. The ordered dither matrix
generation code was moved to dither.c. This function was originally
written by Uoti Urpala.

1 files changed, 77 insertions, 22 deletions

diff --git a/video/out/gl_video.c b/video/out/gl_video.c
index 791f302941..cc2656c763 100644
--- a/video/out/gl_video.c
+++ b/video/out/gl_video.c
@@ -37,6 +37,7 @@
 #include "aspect.h"
 #include "video/memcpy_pic.h"
 #include "bitmap_packer.h"
+#include "dither.h"
 
 static const char vo_opengl_shaders[] =
 // Generated from gl_video_shaders.glsl
@@ -192,6 +193,10 @@ struct gl_video {
 
     int frames_rendered;
 
+    // Cached because computing it can take relatively long
+    int last_dither_matrix_size;
+    float *last_dither_matrix;
+
     void *scratch;
 };
 
@@ -229,6 +234,7 @@ static const char *osd_shaders[SUBBITMAP_COUNT] = {
 static const struct gl_video_opts gl_video_opts_def = {
     .npot = 1,
     .dither_depth = -1,
+    .dither_size = 6,
     .fbo_format = GL_RGB,
     .scale_sep = 1,
     .scalers = { "bilinear", "bilinear" },
@@ -269,6 +275,10 @@ const struct m_sub_options gl_video_conf = {
                     {"rgba32f", GL_RGBA32F})),
         OPT_CHOICE_OR_INT("dither-depth", dither_depth, 0, -1, 16,
                           ({"no", -1}, {"auto", 0})),
+        OPT_CHOICE("dither", dither_algo, 0,
+                   ({"fruit", 0}, {"ordered", 1}, {"no", -1})),
+        OPT_INTRANGE("dither-size-fruit", dither_size, 0, 2, 8),
+        OPT_FLAG("temporal-dither", temporal_dither, 0),
         OPT_FLAG("alpha", enable_alpha, 0),
         {0}
     },
@@ -754,6 +764,7 @@ static void compile_shaders(struct gl_video *p)
     shader_def_opt(&header_final, "USE_3DLUT", p->use_lut_3d);
     shader_def_opt(&header_final, "USE_SRGB", p->opts.srgb);
     shader_def_opt(&header_final, "USE_DITHER", p->dither_texture != 0);
+    shader_def_opt(&header_final, "USE_TEMPORAL_DITHER", p->opts.temporal_dither);
 
     if (p->opts.scale_sep && p->scalers[0].kernel) {
         header_sep = talloc_strdup(tmp, "");
@@ -926,18 +937,6 @@ static void init_scaler(struct gl_video *p, struct scaler *scaler)
     debug_check_gl(p, "after initializing scaler");
 }
 
-static void make_dither_matrix(unsigned char *m, int size)
-{
-    m[0] = 0;
-    for (int sz = 1; sz < size; sz *= 2) {
-        int offset[] = {sz*size, sz, sz * (size+1), 0};
-        for (int i = 0; i < 4; i++)
-            for (int y = 0; y < sz * size; y += size)
-                for (int x = 0; x < sz; x++)
-                    m[x+y+offset[i]] = m[x+y] * 4 + (3-i) * 256/size/size;
-    }
-}
-
 static void init_dither(struct gl_video *p)
 {
     GL *gl = p->gl;
@@ -947,30 +946,54 @@ static void init_dither(struct gl_video *p)
     if (p->opts.dither_depth > 0)
         dst_depth = p->opts.dither_depth;
 
-    if (p->opts.dither_depth < 0)
+    if (p->opts.dither_depth < 0 || p->opts.dither_algo < 0)
         return;
 
     mp_msg(MSGT_VO, MSGL_V, "[gl] Dither to %d.\n", dst_depth);
 
+    int tex_size;
+    void *tex_data;
+    GLenum tex_type;
+    unsigned char temp[256];
+
+    if (p->opts.dither_algo == 0) {
+        int sizeb = p->opts.dither_size;
+        int size = 1 << sizeb;
+
+        if (p->last_dither_matrix_size != size) {
+            p->last_dither_matrix = talloc_realloc(p, p->last_dither_matrix,
+                                                   float, size * size);
+            mp_make_fruit_dither_matrix(p->last_dither_matrix, sizeb);
+            p->last_dither_matrix_size = size;
+        }
+
+        tex_size = size;
+        tex_type = GL_FLOAT;
+        tex_data = p->last_dither_matrix;
+    } else {
+        assert(sizeof(temp) >= 8 * 8);
+        mp_make_ordered_dither_matrix(temp, 8);
+
+        tex_size = 8;
+        tex_type = GL_UNSIGNED_BYTE;
+        tex_data = temp;
+    }
+
     // This defines how many bits are considered significant for output on
-    // screen. The superfluous bits will be used for rounded according to the
+    // screen. The superfluous bits will be used for rounding according to the
     // dither matrix. The precision of the source implicitly decides how many
     // dither patterns can be visible.
     p->dither_quantization = (1 << dst_depth) - 1;
-    int size = 8;
-    p->dither_multiply = p->dither_quantization + 1.0 / (size*size);
-    unsigned char dither[256];
-    make_dither_matrix(dither, size);
-
-    p->dither_size = size;
+    p->dither_multiply = p->dither_quantization + 1.0 / (tex_size * tex_size);
+    p->dither_size = tex_size;
 
     gl->ActiveTexture(GL_TEXTURE0 + TEXUNIT_DITHER);
     gl->GenTextures(1, &p->dither_texture);
     gl->BindTexture(GL_TEXTURE_2D, p->dither_texture);
     gl->PixelStorei(GL_UNPACK_ALIGNMENT, 1);
     gl->PixelStorei(GL_UNPACK_ROW_LENGTH, 0);
-    gl->TexImage2D(GL_TEXTURE_2D, 0, GL_RED, size, size, 0, GL_RED,
-                   GL_UNSIGNED_BYTE, dither);
+    gl->TexImage2D(GL_TEXTURE_2D, 0, GL_RED, tex_size, tex_size, 0, GL_RED,
+                   tex_type, tex_data);
     gl->TexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
     gl->TexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
     gl->TexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
@@ -1164,6 +1187,25 @@ static void uninit_video(struct gl_video *p)
     fbotex_uninit(p, &p->scale_sep_fbo);
 }
 
+static void change_dither_trafo(struct gl_video *p)
+{
+    GL *gl = p->gl;
+    int program = p->final_program;
+
+    int phase = p->frames_rendered % 8u;
+    float r = phase * (M_PI / 2); // rotate
+    float m = phase < 4 ? 1 : -1; // mirror
+
+    gl->UseProgram(program);
+
+    float matrix[2][2] = {{cos(r),     -sin(r)    },
+                          {sin(r) * m,  cos(r) * m}};
+    gl->UniformMatrix2fv(gl->GetUniformLocation(program, "dither_trafo"),
+                         1, GL_TRUE, &matrix[0][0]);
+
+    gl->UseProgram(0);
+}
+
 static void render_to_fbo(struct gl_video *p, struct fbotex *fbo, int w, int h,
                           int tex_w, int tex_h)
 {
@@ -1206,6 +1248,9 @@ void gl_video_render_frame(struct gl_video *p)
     struct video_image *vimg = &p->image;
     bool is_flipped = vimg->image_flipped;
 
+    if (p->opts.temporal_dither)
+        change_dither_trafo(p);
+
     if (p->dst_rect.x0 > p->vp_x || p->dst_rect.y0 > p->vp_y
         || p->dst_rect.x1 < p->vp_x + p->vp_w
         || p->dst_rect.y1 < p->vp_y + p->vp_h)
@@ -1274,6 +1319,8 @@ void gl_video_render_frame(struct gl_video *p)
 
     gl->UseProgram(0);
 
+    p->frames_rendered++;
+
     debug_check_gl(p, "after video rendering");
 }
 
@@ -1542,6 +1589,14 @@ static void check_gl_features(struct gl_video *p)
         }
     }
 
+    if (!have_float_tex && p->opts.dither_depth >= 0) {
+        // only fruit dithering uses float textures
+        if (p->opts.dither_algo == 0) {
+            p->opts.dither_depth = -1;
+            disabled[n_disabled++] = "dithering (float tex.)";
+        }
+    }
+
     if (!have_srgb && p->opts.srgb) {
         p->opts.srgb = false;
         disabled[n_disabled++] = "sRGB";