[gtk/wip/otte/dithered-gradients: 3/3] gsk: Add GSK_DEBUG=no-dither

[Benjamin Otte <otte src gnome org>]

commit 4f8e1133e4d015a23a405b7794e34cdc95fa8c9d
Author: Benjamin Otte <otte redhat com>
Date:   Sat May 28 06:27:24 2022 +0200

    gsk: Add GSK_DEBUG=no-dither
    
    Allows turning off dithering in the GLSL compilers. Useful for
    comparing images, for benchmarking differences and potentially for the
    testsuite.

 gsk/gl/gskglcompiler.c            | 14 ++++++++++----
 gsk/gl/resources/preamble.fs.glsl |  4 ++++
 gsk/gskdebug.c                    |  1 +
 gsk/gskdebugprivate.h             | 11 ++++++-----
 4 files changed, 21 insertions(+), 9 deletions(-)
---
diff --git a/gsk/gl/gskglcompiler.c b/gsk/gl/gskglcompiler.c
index 3449dac50d..ce2074cb28 100644
--- a/gsk/gl/gskglcompiler.c
+++ b/gsk/gl/gskglcompiler.c
@@ -543,6 +543,7 @@ gsk_gl_compiler_compile (GskGLCompiler  *self,
   const char *legacy = "";
   const char *gl3 = "";
   const char *gles = "";
+  const char *dither = "";
   int program_id;
   int vertex_id;
   int fragment_id;
@@ -572,11 +573,14 @@ gsk_gl_compiler_compile (GskGLCompiler  *self,
   if (self->gl3)
     gl3 = "#define GSK_GL3 1\n";
 
+  if (GSK_DEBUG_CHECK (NO_DITHER))
+    dither = "#define GSK_NO_DITHER 1\n";
+
   vertex_id = glCreateShader (GL_VERTEX_SHADER);
   glShaderSource (vertex_id,
-                  10,
+                  11,
                   (const char *[]) {
-                    version, debug, legacy, gl3, gles,
+                    version, debug, legacy, gl3, gles, dither,
                     clip,
                     get_shader_string (self->all_preamble),
                     get_shader_string (self->vertex_preamble),
@@ -589,6 +593,7 @@ gsk_gl_compiler_compile (GskGLCompiler  *self,
                     strlen (legacy),
                     strlen (gl3),
                     strlen (gles),
+                    strlen (dither),
                     strlen (clip),
                     g_bytes_get_size (self->all_preamble),
                     g_bytes_get_size (self->vertex_preamble),
@@ -607,9 +612,9 @@ gsk_gl_compiler_compile (GskGLCompiler  *self,
 
   fragment_id = glCreateShader (GL_FRAGMENT_SHADER);
   glShaderSource (fragment_id,
-                  10,
+                  11,
                   (const char *[]) {
-                    version, debug, legacy, gl3, gles,
+                    version, debug, legacy, gl3, gles, dither,
                     clip,
                     get_shader_string (self->all_preamble),
                     get_shader_string (self->fragment_preamble),
@@ -622,6 +627,7 @@ gsk_gl_compiler_compile (GskGLCompiler  *self,
                     strlen (legacy),
                     strlen (gl3),
                     strlen (gles),
+                    strlen (dither),
                     strlen (clip),
                     g_bytes_get_size (self->all_preamble),
                     g_bytes_get_size (self->fragment_preamble),
diff --git a/gsk/gl/resources/preamble.fs.glsl b/gsk/gl/resources/preamble.fs.glsl
index 189da3aee2..734719adac 100644
--- a/gsk/gl/resources/preamble.fs.glsl
+++ b/gsk/gl/resources/preamble.fs.glsl
@@ -127,6 +127,9 @@ float gsk_interleaved_gradient_noise (vec2 p)
 }
 
 vec4 gskDither(vec4 color) {
+#if defined(GSK_NO_DITHER)
+  return color;
+#else
   if (u_bit_depth > 10)
     return color;
 
@@ -135,6 +138,7 @@ vec4 gskDither(vec4 color) {
   noise = noise / (pow(2.0, u_bit_depth) - 1.0);
   color = vec4(color.rgb + noise, color.a);
   return color;
+#endif
 }
 
 vec4 gsk_get_output_color(vec4 color, float alpha) {
diff --git a/gsk/gskdebug.c b/gsk/gskdebug.c
index 83a3619fe7..f18c5a59ba 100644
--- a/gsk/gskdebug.c
+++ b/gsk/gskdebug.c
@@ -10,6 +10,7 @@ static const GdkDebugKey gsk_debug_keys[] = {
   { "surface", GSK_DEBUG_SURFACE, "Information about surfaces" },
   { "fallback", GSK_DEBUG_FALLBACK, "Information about fallbacks" },
   { "glyphcache", GSK_DEBUG_GLYPH_CACHE, "Information about glyph caching" },
+  { "no-dither", GSK_DEBUG_NO_DITHER, "Disable dithering" },
   { "geometry", GSK_DEBUG_GEOMETRY, "Show borders (when using cairo)" },
   { "full-redraw", GSK_DEBUG_FULL_REDRAW, "Force full redraws" },
   { "sync", GSK_DEBUG_SYNC, "Sync after each frame" },
diff --git a/gsk/gskdebugprivate.h b/gsk/gskdebugprivate.h
index 345c1555ab..9320a471a9 100644
--- a/gsk/gskdebugprivate.h
+++ b/gsk/gskdebugprivate.h
@@ -15,11 +15,12 @@ typedef enum {
   GSK_DEBUG_FALLBACK              = 1 <<  6,
   GSK_DEBUG_GLYPH_CACHE           = 1 <<  7,
   /* flags below may affect behavior */
-  GSK_DEBUG_GEOMETRY              = 1 <<  9,
-  GSK_DEBUG_FULL_REDRAW           = 1 << 10,
-  GSK_DEBUG_SYNC                  = 1 << 11,
-  GSK_DEBUG_VULKAN_STAGING_IMAGE  = 1 << 12,
-  GSK_DEBUG_VULKAN_STAGING_BUFFER = 1 << 13
+  GSK_DEBUG_NO_DITHER             = 1 <<  9,
+  GSK_DEBUG_GEOMETRY              = 1 << 10,
+  GSK_DEBUG_FULL_REDRAW           = 1 << 11,
+  GSK_DEBUG_SYNC                  = 1 << 12,
+  GSK_DEBUG_VULKAN_STAGING_IMAGE  = 1 << 13,
+  GSK_DEBUG_VULKAN_STAGING_BUFFER = 1 << 14
 } GskDebugFlags;
 
 #define GSK_DEBUG_ANY ((1 << 13) - 1)