(Reland) Fix extraction of colour components in CPDF_DIBSource::DownSampleScanline32Bit

Previously, if |m_bpc| was < 8 (e.g. 4), this function may still try to
access the source components as if |m_bpc| == 8. Even when it fell into
the codepath that tried to do the right thing in this case, it was
wrong.

BUG=554151
R=tsepez@chromium.org, thestig@chromium.org

Committed: https://pdfium.googlesource.com/pdfium/+/9b99615806e358fdb396d1cb162ee2e69c2a20ec

Review URL: https://codereview.chromium.org/1433423002 .

1 files changed, 19 insertions, 0 deletions

diff --git a/core/src/fpdfapi/fpdf_render/fpdf_render_loadimage_embeddertest.cpp b/core/src/fpdfapi/fpdf_render/fpdf_render_loadimage_embeddertest.cpp
new file mode 100644
index 0000000000..1633249d0d
--- /dev/null
+++ b/core/src/fpdfapi/fpdf_render/fpdf_render_loadimage_embeddertest.cpp
@@ -0,0 +1,19 @@
+// Copyright 2015 PDFium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "testing/embedder_test.h"
+#include "testing/gtest/include/gtest/gtest.h"
+
+class FPDFRenderLoadImageEmbeddertest : public EmbedderTest {};
+
+TEST_F(FPDFRenderLoadImageEmbeddertest, Bug_554151) {
+  // Test scanline downsampling with a BitsPerComponent of 4.
+  // Should not crash.
+  EXPECT_TRUE(OpenDocument("bug_554151.pdf"));
+  FPDF_PAGE page = LoadPage(0);
+  EXPECT_NE(nullptr, page);
+  FPDF_BITMAP bitmap = RenderPage(page);
+  FPDFBitmap_Destroy(bitmap);
+  UnloadPage(page);
+}