Add Chromium-only Blender WebEngine parity work

blender-5.2.0/source/blender/imbuf/intern/imageprocess.cc

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+/* SPDX-FileCopyrightText: 2001-2002 NaN Holding BV. All rights reserved.
+ * SPDX-FileCopyrightText: 2024 Blender Authors
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later */
+
+/** \file
+ * \ingroup imbuf
+ */
+
+#include "BLI_math_vector.h"
+#include "BLI_task.hh"
+
+#include "IMB_imbuf.hh"
+#include "IMB_imbuf_types.hh"
+
+namespace blender {
+
+/* -------------------------------------------------------------------- */
+/** \name Alpha-under
+ * \{ */
+
+void IMB_alpha_under_color_float(float *rect_float, int x, int y, float backcol[3])
+{
+  threading::parallel_for(IndexRange(int64_t(x) * y), 32 * 1024, [&](const IndexRange i_range) {
+    float *pix = rect_float + i_range.first() * 4;
+    for ([[maybe_unused]] const int i : i_range) {
+      const float mul = 1.0f - pix[3];
+      madd_v3_v3fl(pix, backcol, mul);
+      pix[3] = 1.0f;
+      pix += 4;
+    }
+  });
+}
+
+void IMB_alpha_under_color_byte(uchar *rect, int x, int y, const float backcol[3])
+{
+  threading::parallel_for(IndexRange(int64_t(x) * y), 32 * 1024, [&](const IndexRange i_range) {
+    uchar *pix = rect + i_range.first() * 4;
+    for ([[maybe_unused]] const int i : i_range) {
+      if (pix[3] == 255) {
+        /* pass */
+      }
+      else if (pix[3] == 0) {
+        pix[0] = backcol[0] * 255;
+        pix[1] = backcol[1] * 255;
+        pix[2] = backcol[2] * 255;
+      }
+      else {
+        float alpha = pix[3] / 255.0;
+        float mul = 1.0f - alpha;
+
+        pix[0] = (pix[0] * alpha) + mul * backcol[0];
+        pix[1] = (pix[1] * alpha) + mul * backcol[1];
+        pix[2] = (pix[2] * alpha) + mul * backcol[2];
+      }
+      pix[3] = 255;
+      pix += 4;
+    }
+  });
+}
+
+/** \} */
+
+}  // namespace blender