Bug 1593094. Add glyph flashing pref. r=kvark

This makes it easier to debug glyph rasterization issues

Differential Revision: https://phabricator.services.mozilla.com/D51310

--HG--
extra : moz-landing-system : lando

gfx/thebes/gfxPlatform.cpp

@@ -601,6 +601,7 @@ static void WebRenderDebugPrefChangeCallback(const char* aPrefName, void*) {
   GFX_WEBRENDER_DEBUG(".disable-gradient-prims",
                       wr::DebugFlags_DISABLE_GRADIENT_PRIMS)
   GFX_WEBRENDER_DEBUG(".obscure-images", wr::DebugFlags_OBSCURE_IMAGES)
+  GFX_WEBRENDER_DEBUG(".glyph-flashing", wr::DebugFlags_GLYPH_FLASHING)
 #undef GFX_WEBRENDER_DEBUG
 
   gfx::gfxVars::SetWebRenderDebugFlags(flags.bits);

gfx/wr/webrender/src/glyph_rasterizer/mod.rs

@@ -24,11 +24,15 @@ use rayon::prelude::*;
 use euclid::approxeq::ApproxEq;
 use euclid::size2;
 use std::cmp;
+use std::cell::Cell;
 use std::hash::{Hash, Hasher};
 use std::mem;
 use std::ops::Deref;
 use std::sync::{Arc, Condvar, Mutex, MutexGuard};
 use std::sync::mpsc::{channel, Receiver, Sender};
+use std::sync::atomic::{AtomicBool, Ordering};
+
+pub static GLYPH_FLASHING: AtomicBool = AtomicBool::new(false);
 
 impl FontContexts {
     /// Get access to the font context associated to the current thread.
@@ -42,8 +46,19 @@ impl FontContexts {
     }
 }
 
-impl GlyphRasterizer {
+thread_local! {
+    pub static SEED: Cell<u32> = Cell::new(0);
+}
 
+// super simple random to avoid dependency on rand
+fn random() -> u32 {
+    SEED.with(|seed| {
+        seed.set(seed.get().wrapping_mul(22695477).wrapping_add(1));
+        seed.get()
+    })
+}
+
+impl GlyphRasterizer {
     pub fn request_glyphs(
         &mut self,
         glyph_cache: &mut GlyphCache,
@@ -118,6 +133,22 @@ impl GlyphRasterizer {
                             glyph.bytes.len(),
                             bpp * (glyph.width * glyph.height) as usize
                         );
+
+                        // a quick-and-dirty monochrome over
+                        fn over(dst: u8, src: u8) -> u8 {
+                            let a = src as u32;
+                            let a = 256 - a;
+                            let dst = ((dst as u32 * a) >> 8) as u8;
+                            src + dst
+                        }
+
+                        if GLYPH_FLASHING.load(Ordering::Relaxed) {
+                            let color = (random() & 0xff) as u8;
+                            for i in &mut glyph.bytes {
+                                *i = over(*i, color);
+                            }
+                        }
+
                         assert_eq!((glyph.left.fract(), glyph.top.fract()), (0.0, 0.0));
 
                         // Check if the glyph has a bitmap that needs to be downscaled.

gfx/wr/webrender/src/resource_cache.rs

@@ -21,7 +21,7 @@ use crate::device::TextureFilter;
 use euclid::{point2, size2};
 use crate::glyph_cache::GlyphCache;
 use crate::glyph_cache::GlyphCacheEntry;
-use crate::glyph_rasterizer::{BaseFontInstance, FontInstance, GlyphFormat, GlyphKey, GlyphRasterizer};
+use crate::glyph_rasterizer::{GLYPH_FLASHING, BaseFontInstance, FontInstance, GlyphFormat, GlyphKey, GlyphRasterizer};
 use crate::gpu_cache::{GpuCache, GpuCacheAddress, GpuCacheHandle};
 use crate::gpu_types::UvRectKind;
 use crate::image::{compute_tile_size, compute_tile_rect, compute_tile_range, for_each_tile_in_range};
@@ -1856,6 +1856,7 @@ impl ResourceCache {
     }
 
     pub fn set_debug_flags(&mut self, flags: DebugFlags) {
+        GLYPH_FLASHING.store(flags.contains(DebugFlags::GLYPH_FLASHING), std::sync::atomic::Ordering::Relaxed);
         self.texture_cache.set_debug_flags(flags);
     }
 

gfx/wr/webrender_api/src/api.rs

@@ -1142,6 +1142,7 @@ bitflags! {
         const DISABLE_TEXT_PRIMS = 1 << 22;
         const DISABLE_GRADIENT_PRIMS = 1 << 23;
         const OBSCURE_IMAGES = 1 << 24;
+        const GLYPH_FLASHING = 1 << 25;
         /// The profiler only displays information that is out of the ordinary.
         const SMART_PROFILER        = 1 << 26;
         /// Dynamically control whether picture caching is enabled.

modules/libpref/init/all.js

@@ -673,6 +673,7 @@ pref("gfx.webrender.debug.picture-caching", false);
 pref("gfx.webrender.debug.primitives", false);
 pref("gfx.webrender.debug.small-screen", false);
 pref("gfx.webrender.debug.obscure-images", false);
+pref("gfx.webrender.debug.glyph-flashing", false);
 
 pref("accessibility.warn_on_browsewithcaret", true);