2 files changed, 35 insertions, 1 deletions
diff --git a/core/fpdfapi/page/cpdf_page.cpp b/core/fpdfapi/page/cpdf_page.cpp
index dfbd342f13..6213e5fccb 100644
--- a/core/fpdfapi/page/cpdf_page.cpp
+++ b/core/fpdfapi/page/cpdf_page.cpp
@@ -178,6 +178,35 @@ CFX_Matrix CPDF_Page::GetDisplayMatrix(int xPos,
   return matrix;
 }
 
+// This method follows the same apparent logic as GetDisplayMatrix(). For
+// example, consider point 0. First, take the top left coordinate of the
+// rectangle in the transformed space. Now, calculate what this point was in the
+// original space by inverting. Note that this is not necessarily the same as
+// the top left corner of the original rectangle.
+CFX_Matrix CPDF_Page::GetDisplayMatrixWithTransformation(
+    int xPos,
+    int yPos,
+    int xSize,
+    int ySize,
+    const CFX_Matrix& transformation) {
+  CFX_FloatRect rect(xPos, yPos, xPos + xSize, yPos + ySize);
+  rect = transformation.TransformRect(rect);
+  CFX_Matrix inverse = transformation.GetInverse();
+  CFX_PointF point0(rect.left, rect.top);
+  CFX_PointF point1(rect.left, rect.bottom);
+  CFX_PointF point2(rect.right, rect.top);
+  point0 = inverse.Transform(point0);
+  point1 = inverse.Transform(point1);
+  point2 = inverse.Transform(point2);
+
+  CFX_Matrix matrix = m_PageMatrix;
+  matrix.Concat(CFX_Matrix(
+      (point2.x - point0.x) / m_PageWidth, (point2.y - point0.y) / m_PageWidth,
+      (point1.x - point0.x) / m_PageHeight,
+      (point1.y - point0.y) / m_PageHeight, point0.x, point0.y));
+  return matrix;
+}
+
 int CPDF_Page::GetPageRotation() const {
   CPDF_Object* pRotate = GetPageAttr("Rotate");
   int rotate = pRotate ? (pRotate->GetInteger() / 90) % 4 : 0;
diff --git a/core/fpdfapi/page/cpdf_page.h b/core/fpdfapi/page/cpdf_page.h
index 1891e651be..47fba3caec 100644
--- a/core/fpdfapi/page/cpdf_page.h
+++ b/core/fpdfapi/page/cpdf_page.h
@@ -38,11 +38,16 @@ class CPDF_Page : public CPDF_PageObjectHolder {
                               int xSize,
                               int ySize,
                               int iRotate) const;
+  CFX_Matrix GetDisplayMatrixWithTransformation(
+      int xPos,
+      int yPos,
+      int xSize,
+      int ySize,
+      const CFX_Matrix& transformation);
 
   float GetPageWidth() const { return m_PageWidth; }
   float GetPageHeight() const { return m_PageHeight; }
   CFX_FloatRect GetPageBBox() const { return m_BBox; }
-  const CFX_Matrix& GetPageMatrix() const { return m_PageMatrix; }
   int GetPageRotation() const;
   CPDF_PageRenderCache* GetRenderCache() const { return m_pPageRender.get(); }