SkColorSpaceXformSteps

Lots TODO.

Change-Id: I95edb764b85a5140d432adb506c3b537869e6df4
Reviewed-on: https://skia-review.googlesource.com/129933
Commit-Queue: Mike Klein <mtklein@chromium.org>
Reviewed-by: Brian Osman <brianosman@google.com>
Auto-Submit: Mike Klein <mtklein@chromium.org>

2 files changed, 116 insertions, 0 deletions

diff --git a/src/core/SkColorSpaceXformSteps.cpp b/src/core/SkColorSpaceXformSteps.cpp
new file mode 100644
index 0000000000..0067a70934
--- /dev/null
+++ b/src/core/SkColorSpaceXformSteps.cpp
@@ -0,0 +1,74 @@
+/*
+ * Copyright 2018 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "SkColorSpaceXformSteps.h"
+
+// Our logical flow modulo any optimization is:
+//   For source colors:
+//    1) get colors into linear, unpremul format
+//    2) transform to dst gamut
+//    3) encode with dst transfer function if dst has non-linear blending
+//    4) premul so we can blend
+//
+//   For destination colors:
+//    a) Linearize if dst has linear blending
+//    b) (Presumably all destinations are already premul, but logically, premul here)
+//
+//   Now the source and destination pipelines unify:
+//    I)  blend the src and dst colors, which are encoded the same way in the same gamut
+//    II) if dst has linear blending, encode using dst transfer function
+//
+//  Step 1) is represented by three bits:
+//     - early_unpremul, converting f(s)*a,a to f(s),a if src has non-linear blending
+//     - linearize_src,  converting f(s),a to s,a   _or_  f(s*a),a to s*a,a
+//     - late_unpremul,  converting s*a,a to s,a if src has linear blending
+//  So we'll either early_unpremul and linearize_src, or linearize_src and late_unpremul.
+//
+
+SkColorSpaceXformSteps::SkColorSpaceXformSteps(SkColorSpace* src, SkAlphaType srcAT,
+                                               SkColorSpace* dst) {
+    // Set all bools to false, all floats to 0.0f.
+    memset(this, 0, sizeof(*this));
+
+    // We have some options about what to do with null src or dst here.
+#if 1
+    SkASSERT(src && dst);
+#else
+    // If either the source or destination color space is unspecified,
+    // treat it as non-linearly-blended sRGB ("legacy").
+    sk_sp<SkColorSpace> sRGB_NL;
+    if (!src || !dst) {
+        sRGB_NL = SkColorSpace::MakeSRGB()->makeNonlinearBlending();
+        if (!src) { src = sRGB_NL.get(); }
+        if (!dst) { dst = sRGB_NL.get(); }
+    }
+#endif
+
+    bool srcNL = src->nonlinearBlending(),
+         srcPM = srcAT == kPremul_SkAlphaType,
+         dstNL = dst->nonlinearBlending();
+
+    // Step 1)  get source colors into linear, unpremul format
+    this->early_unpremul =  srcNL && srcPM;
+    this->linearize_src  =   true;
+    this->late_unpremul  = !srcNL && srcPM;
+
+    // Step 2)  transform source colors into destination gamut
+    this->gamut_transform = true;
+
+    // Step 3)  encode with dst transfer function if dst has non-linear blending
+    this->early_encode = dstNL;
+
+    // Step 4)  premul so we can blend
+    this->premul = true || !srcPM;
+
+    // Step a)  linearize if dst has linear blending
+    this->linearize_dst = !dstNL;
+
+    // Step II) if dst has linear blending, encode back using dst transfer function before storing
+    this->late_encode = !dstNL;
+}
diff --git a/src/core/SkColorSpaceXformSteps.h b/src/core/SkColorSpaceXformSteps.h
new file mode 100644
index 0000000000..03702d813a
--- /dev/null
+++ b/src/core/SkColorSpaceXformSteps.h
@@ -0,0 +1,42 @@
+/*
+ * Copyright 2018 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef SkColorSpaceXformSteps_DEFINED
+#define SkColorSpaceXformSteps_DEFINED
+
+#include "SkColorSpace.h"
+#include "SkImageInfo.h"
+
+struct SkColorSpaceXformSteps {
+    SkColorSpaceXformSteps(SkColorSpace* src, SkAlphaType srcAT,
+                           SkColorSpace* dst);
+
+    // Source pipeline steps, pre-blend.
+    bool early_unpremul;
+    bool linearize_src;
+    bool late_unpremul;
+    bool gamut_transform;
+    bool early_encode;
+    bool premul;
+
+    // Destination pipeline steps, pre-blend.
+    bool linearize_dst;
+
+    // Post-blend steps.
+    bool late_encode;
+
+/* TODO
+    SkColorSpaceTransferFn srcTFInv,  // Apply for linearize_src.
+                           dstTFInv,  // Apply for linearize_dst.
+                           dstTF;     // Apply for early_encode or late_encode.
+    float src_to_dst_matrix[9];       // Apply this 3x3 row-major matrix for gamut_transform.
+*/
+};
+
+
+
+#endif//SkColorSpaceXformSteps_DEFINED