Correctly render ISO gainmapped images

* Apply the gainmap in reverse when using an HDR base image
* Support alternative primaries
* Nudge the guards that optimize away applying the gainmap shader

Bug: 349357636
Flag: com.android.graphics.hwui.flags.iso_gainmap_apis
Test: GainmapTests
Change-Id: I230a765feddb306330e643e6ead8e62719f49ee5
diff --git a/libs/hwui/SkiaCanvas.cpp b/libs/hwui/SkiaCanvas.cpp
index 7c15086..7f5ca44 100644
--- a/libs/hwui/SkiaCanvas.cpp
+++ b/libs/hwui/SkiaCanvas.cpp
@@ -622,18 +622,13 @@
     auto colorSpace = info.colorSpace();
     // If we don't have a colorspace, we can't apply a gainmap
     if (!colorSpace) return false;
-    skcms_TransferFunction tfn;
-    colorSpace->transferFn(&tfn);
 
-    auto transferType = skcms_TransferFunction_getType(&tfn);
-    switch (transferType) {
-        case skcms_TFType_HLGish:
-        case skcms_TFType_HLGinvish:
-        case skcms_TFType_PQish:
-            return true;
-        case skcms_TFType_Invalid:
-        case skcms_TFType_sRGBish:
-            return false;
+    const float targetRatio = uirenderer::getTargetHdrSdrRatio(colorSpace);
+
+    if (bitmap.gainmap()->info.fBaseImageType == SkGainmapInfo::BaseImageType::kHDR) {
+        return targetRatio < bitmap.gainmap()->info.fDisplayRatioHdr;
+    } else {
+        return targetRatio > bitmap.gainmap()->info.fDisplayRatioSdr;
     }
 }