Color management: Improve no-op color space detection

Make it so transform between color spaces which is a no-op does not
peroform any calculations.

This was initially found when working on #110941, but the issue can
be replicated easily by renaming "Linear" to "Linear Rec.709" and
adding alias as "Linear".

Doing so would result in a failure of the compositor_matte_test.
The reason for that is due to the image data-block still referring
to the "Linear" color space, the name-based comparison not detecting
that "Linear" and "Linear Rec.709" are the same spaces, and that the
cryptomatte requires bit-perfect floating point values.

Pull Request: https://projects.blender.org/blender/blender/pulls/110959

intern/opencolorio/fallback_impl.cc

@@ -77,6 +77,12 @@ struct FallbackTransform {
     applyRGB(pixel);
   }
 
+  bool isNoOp()
+  {
+    /* Rely on the short-circuiting based on name-space comparison in the IMB_colormanagement. */
+    return false;
+  }
+
   TransformType type;
   /* Scale transform. */
   float scale;
@@ -99,6 +105,11 @@ struct FallbackProcessor {
     transform.applyRGBA(pixel);
   }
 
+  bool isNoOp()
+  {
+    return transform.isNoOp();
+  }
+
   FallbackTransform transform;
 
   MEM_CXX_CLASS_ALLOC_FUNCS("FallbackProcessor");
@@ -337,6 +348,11 @@ void FallbackImpl::processorRelease(OCIO_ConstProcessorRcPtr *processor)
   delete (FallbackProcessor *)(processor);
 }
 
+bool FallbackImpl::cpuProcessorIsNoOp(OCIO_ConstCPUProcessorRcPtr *cpu_processor)
+{
+  return ((FallbackProcessor *)cpu_processor)->isNoOp();
+}
+
 void FallbackImpl::cpuProcessorApply(OCIO_ConstCPUProcessorRcPtr *cpu_processor,
                                      OCIO_PackedImageDesc *img)
 {

intern/opencolorio/ocio_capi.cc

@@ -189,6 +189,11 @@ OCIO_ConstCPUProcessorRcPtr *OCIO_processorGetCPUProcessor(OCIO_ConstProcessorRc
   return impl->processorGetCPUProcessor(processor);
 }
 
+bool OCIO_cpuProcessorIsNoOp(OCIO_ConstCPUProcessorRcPtr *cpu_processor)
+{
+  return impl->cpuProcessorIsNoOp(cpu_processor);
+}
+
 void OCIO_cpuProcessorApply(OCIO_ConstCPUProcessorRcPtr *cpu_processor, OCIO_PackedImageDesc *img)
 {
   impl->cpuProcessorApply(cpu_processor, img);

intern/opencolorio/ocio_capi.h

@@ -151,6 +151,7 @@ OCIO_ConstProcessorRcPtr *OCIO_configGetProcessorWithNames(OCIO_ConstConfigRcPtr
 void OCIO_processorRelease(OCIO_ConstProcessorRcPtr *cpu_processor);
 
 OCIO_ConstCPUProcessorRcPtr *OCIO_processorGetCPUProcessor(OCIO_ConstProcessorRcPtr *processor);
+bool OCIO_cpuProcessorIsNoOp(OCIO_ConstCPUProcessorRcPtr *cpu_processor);
 void OCIO_cpuProcessorApply(OCIO_ConstCPUProcessorRcPtr *cpu_processor,
                             struct OCIO_PackedImageDesc *img);
 void OCIO_cpuProcessorApply_predivide(OCIO_ConstCPUProcessorRcPtr *cpu_processor,

intern/opencolorio/ocio_impl.cc

@@ -590,6 +590,11 @@ void OCIOImpl::cpuProcessorApply_predivide(OCIO_ConstCPUProcessorRcPtr *cpu_proc
   }
 }
 
+bool OCIOImpl::cpuProcessorIsNoOp(OCIO_ConstCPUProcessorRcPtr *cpu_processor)
+{
+  return (*(ConstCPUProcessorRcPtr *)cpu_processor)->isNoOp();
+}
+
 void OCIOImpl::cpuProcessorApplyRGB(OCIO_ConstCPUProcessorRcPtr *cpu_processor, float *pixel)
 {
   (*(ConstCPUProcessorRcPtr *)cpu_processor)->applyRGB(pixel);

intern/opencolorio/ocio_impl.h

@@ -63,6 +63,7 @@ class IOCIOImpl {
   virtual void processorRelease(OCIO_ConstProcessorRcPtr *processor) = 0;
 
   virtual OCIO_ConstCPUProcessorRcPtr *processorGetCPUProcessor(OCIO_ConstProcessorRcPtr *p) = 0;
+  virtual bool cpuProcessorIsNoOp(OCIO_ConstCPUProcessorRcPtr *cpu_processor) = 0;
   virtual void cpuProcessorApply(OCIO_ConstCPUProcessorRcPtr *cpu_processor,
                                  OCIO_PackedImageDesc *img) = 0;
   virtual void cpuProcessorApply_predivide(OCIO_ConstCPUProcessorRcPtr *cpu_processor,
@@ -177,6 +178,7 @@ class FallbackImpl : public IOCIOImpl {
   void processorRelease(OCIO_ConstProcessorRcPtr *processor);
 
   OCIO_ConstCPUProcessorRcPtr *processorGetCPUProcessor(OCIO_ConstProcessorRcPtr *processor);
+  bool cpuProcessorIsNoOp(OCIO_ConstCPUProcessorRcPtr *cpu_processor);
   void cpuProcessorApply(OCIO_ConstCPUProcessorRcPtr *cpu_processor, OCIO_PackedImageDesc *img);
   void cpuProcessorApply_predivide(OCIO_ConstCPUProcessorRcPtr *cpu_processor,
                                    OCIO_PackedImageDesc *img);
@@ -267,6 +269,7 @@ class OCIOImpl : public IOCIOImpl {
   void processorRelease(OCIO_ConstProcessorRcPtr *processor);
 
   OCIO_ConstCPUProcessorRcPtr *processorGetCPUProcessor(OCIO_ConstProcessorRcPtr *processor);
+  bool cpuProcessorIsNoOp(OCIO_ConstCPUProcessorRcPtr *cpu_processor);
   void cpuProcessorApply(OCIO_ConstCPUProcessorRcPtr *cpu_processor, OCIO_PackedImageDesc *img);
   void cpuProcessorApply_predivide(OCIO_ConstCPUProcessorRcPtr *cpu_processor,
                                    OCIO_PackedImageDesc *img);

source/blender/imbuf/IMB_colormanagement.h

@@ -421,6 +421,7 @@ struct ColormanageProcessor *IMB_colormanagement_display_processor_new(
     const struct ColorManagedDisplaySettings *display_settings);
 struct ColormanageProcessor *IMB_colormanagement_colorspace_processor_new(
     const char *from_colorspace, const char *to_colorspace);
+bool IMB_colormanagement_processor_is_noop(struct ColormanageProcessor *cm_processor);
 void IMB_colormanagement_processor_apply_v4(struct ColormanageProcessor *cm_processor,
                                             float pixel[4]);
 void IMB_colormanagement_processor_apply_v4_predivide(struct ColormanageProcessor *cm_processor,

source/blender/imbuf/intern/colormanagement.cc

@@ -1930,8 +1930,6 @@ static void colormanagement_transform_ex(uchar *byte_buffer,
                                          bool predivide,
                                          bool do_threaded)
 {
-  ColormanageProcessor *cm_processor;
-
   if (from_colorspace[0] == '\0') {
     return;
   }
@@ -1943,7 +1941,12 @@ static void colormanagement_transform_ex(uchar *byte_buffer,
     return;
   }
 
-  cm_processor = IMB_colormanagement_colorspace_processor_new(from_colorspace, to_colorspace);
+  ColormanageProcessor *cm_processor = IMB_colormanagement_colorspace_processor_new(
+      from_colorspace, to_colorspace);
+  if (IMB_colormanagement_processor_is_noop(cm_processor)) {
+    IMB_colormanagement_processor_free(cm_processor);
+    return;
+  }
 
   if (do_threaded) {
     processor_transform_apply_threaded(
@@ -3851,6 +3854,18 @@ ColormanageProcessor *IMB_colormanagement_colorspace_processor_new(const char *f
   return cm_processor;
 }
 
+bool IMB_colormanagement_processor_is_noop(ColormanageProcessor *cm_processor)
+{
+  if (cm_processor->curve_mapping) {
+    /* Consider processor which has curve mapping as a non no-op.
+     * This is mainly for the simplicity of the check, since the current cases where this function
+     * is used the curve mapping is never assigned. */
+    return false;
+  }
+
+  return OCIO_cpuProcessorIsNoOp(cm_processor->cpu_processor);
+}
+
 void IMB_colormanagement_processor_apply_v4(ColormanageProcessor *cm_processor, float pixel[4])
 {
   if (cm_processor->curve_mapping) {