From cdab015e4485481aaa7a6a63412c715a4dffb925 Mon Sep 17 00:00:00 2001
From: Brian Salomon <bsalomon@google.com>
Date: Fri, 29 Jul 2022 12:55:47 -0400
Subject: [ganesh] Fix double application of local matrices to runtime shaders.

Bug: skia:13598
Change-Id: Iddfb4f43940fd18a10dc7910f111e1f8f49e8e4c
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/563122
Commit-Queue: Brian Salomon <bsalomon@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>

Bug: 240718331
Test: I63f23f412d1b16643053dbcc041ca8f8c800f158
Change-Id: I6c660da30962c76462f70731d075762a9e16beed
Merged-In: Ic90fdcfc89f653caca519ea5655848f309a51312
---
 gm/runtimeshader.cpp         | 47 ++++++++++++++++++++++++++++++++++++++++++++
 src/core/SkRuntimeEffect.cpp |  5 ++++-
 2 files changed, 51 insertions(+), 1 deletion(-)

diff --git a/gm/runtimeshader.cpp b/gm/runtimeshader.cpp
index 94b3e0d4c2..bd865ceabe 100644
--- a/gm/runtimeshader.cpp
+++ b/gm/runtimeshader.cpp
@@ -889,3 +889,50 @@ DEF_SIMPLE_GM(lit_shader_linear_rt, canvas, 512, 256) {
     // Now draw the offscreen surface back to our original canvas:
     canvas->drawImage(surface->makeImageSnapshot(), 0, 0);
 }
+
+// skbug.com/13598 GPU was double applying the local matrix.
+DEF_SIMPLE_GM(local_matrix_shader_rt, canvas, 256, 256) {
+    SkString passthrough(R"(
+        uniform shader s;
+        half4 main(float2 p) { return s.eval(p); }
+    )");
+    auto [rte, error] = SkRuntimeEffect::MakeForShader(passthrough, {});
+    if (!rte) {
+        SkDebugf("%s\n", error.c_str());
+        return;
+    }
+
+    auto image     = GetResourceAsImage("images/mandrill_128.png");
+    auto imgShader = image->makeShader(SkSamplingOptions{});
+
+    auto r = SkRect::MakeWH(image->width(), image->height());
+
+    auto lm = SkMatrix::RotateDeg(90.f, {image->width()/2.f, image->height()/2.f});
+
+    SkPaint paint;
+
+    // image
+    paint.setShader(imgShader);
+    canvas->drawRect(r, paint);
+
+    // passthrough(image)
+    canvas->save();
+    canvas->translate(image->width(), 0);
+    paint.setShader(rte->makeShader(nullptr, &imgShader, 1));
+    canvas->drawRect(r, paint);
+    canvas->restore();
+
+    // localmatrix(image)
+    canvas->save();
+    canvas->translate(0, image->height());
+    paint.setShader(imgShader->makeWithLocalMatrix(lm));
+    canvas->drawRect(r, paint);
+    canvas->restore();
+
+    // localmatrix(passthrough(image)) This was the bug.
+    canvas->save();
+    canvas->translate(image->width(), image->height());
+    paint.setShader(rte->makeShader(nullptr, &imgShader, 1)->makeWithLocalMatrix(lm));
+    canvas->drawRect(r, paint);
+    canvas->restore();
+}
diff --git a/src/core/SkRuntimeEffect.cpp b/src/core/SkRuntimeEffect.cpp
index 3e5543cad1..1c08fb84d4 100644
--- a/src/core/SkRuntimeEffect.cpp
+++ b/src/core/SkRuntimeEffect.cpp
@@ -1133,13 +1133,16 @@ public:
                 get_xformed_uniforms(fEffect.get(), fUniforms, args.fDstColorInfo->colorSpace());
         SkASSERT(uniforms);
 
+        // We handle the pre-local matrix at this level so strip it out.
+        GrFPArgs fpArgs = args;
+        fpArgs.fPreLocalMatrix = nullptr;
         auto [success, fp] = make_effect_fp(fEffect,
                                             "runtime_shader",
                                             std::move(uniforms),
                                             /*inputFP=*/nullptr,
                                             /*destColorFP=*/nullptr,
                                             SkMakeSpan(fChildren),
-                                            args);
+                                            fpArgs);
         if (!success) {
             return nullptr;
         }
-- 
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