Bug 1701758. Avoid identity sRGB transforms. r=aosmond

This avoids the performance cost and ensures the data remains unchanged.

Differential Revision: https://phabricator.services.mozilla.com/D110289

gfx/qcms/qcms.h

@@ -168,6 +168,7 @@ void qcms_profile_release(qcms_profile *profile);
 bool qcms_profile_is_bogus(qcms_profile *profile);
 qcms_intent qcms_profile_get_rendering_intent(qcms_profile *profile);
 icColorSpaceSignature qcms_profile_get_color_space(qcms_profile *profile);
+bool qcms_profile_is_sRGB(qcms_profile *profile);
 
 void qcms_profile_precache_output_transform(qcms_profile *profile);
 

gfx/qcms/src/c_bindings.rs

@@ -89,6 +89,10 @@ pub extern "C" fn qcms_profile_get_rendering_intent(profile: &Profile) -> Intent
 pub extern "C" fn qcms_profile_get_color_space(profile: &Profile) -> icColorSpaceSignature {
     profile.color_space
 }
+#[no_mangle]
+pub extern "C" fn qcms_profile_is_sRGB(profile: &Profile) -> bool {
+    profile.is_sRGB()
+}
 
 #[no_mangle]
 pub unsafe extern "C" fn qcms_profile_release(profile: *mut Profile) {

gfx/qcms/src/iccread.rs

@@ -62,6 +62,7 @@ pub struct Profile {
     pub(crate) output_table_r: Option<Arc<PrecacheOuput>>,
     pub(crate) output_table_g: Option<Arc<PrecacheOuput>>,
     pub(crate) output_table_b: Option<Arc<PrecacheOuput>>,
+    is_srgb: Option<bool>,
 }
 
 #[derive(Default)]
@@ -1009,7 +1010,14 @@ impl Profile {
         let D65 = qcms_white_point_sRGB();
         let table = build_sRGB_gamma_table(1024);
 
-        Profile::new_rgb_with_table(D65, Rec709Primaries, &table).unwrap()
+        let mut srgb = Profile::new_rgb_with_table(D65, Rec709Primaries, &table).unwrap();
+        srgb.is_srgb = Some(true);
+        srgb
+    }
+
+    /// Returns true if this profile is sRGB
+    pub fn is_sRGB(&self) -> bool {
+        matches!(self.is_srgb, Some(true))
     }
 
     /// Create a new profile with D50 adopted white and identity transform functions

image/Decoder.cpp

@@ -113,6 +113,10 @@ qcms_transform* Decoder::GetCMSsRGBTransform(SurfaceFormat aFormat) const {
     // color management entirely.
     return nullptr;
   }
+  if (qcms_profile_is_sRGB(gfxPlatform::GetCMSOutputProfile())) {
+    // Device space is sRGB so we can skip color management as well.
+    return nullptr;
+  }
 
   switch (aFormat) {
     case SurfaceFormat::B8G8R8A8: