From 4721524cb5a91fd57032737c09d40d34f87f4c99 Mon Sep 17 00:00:00 2001
From: Julian Harnath <julian.harnath@rwth-aachen.de>
Date: Tue, 10 Nov 2015 22:22:32 +0100
Subject: [PATCH] BAffineTransform: add PreTranslate/PreScale/PreRotate

* The existing methods TranslateBy(), ScaleBy() and RotateBy()
  transform the transformation. For a transform A, a point p,
  and the temporary transform B (being applied by the methods),
  this results in p' = B*(A*p) = (B*A)*p
  This is not necessarily the desired result. Suppose A is a
  translation and B a rotation, added by RotateBy(). Then B*A
  means that the translation itself is rotated, so B moves the
  coordinate origin itself, by rotating it around the original
  origin of the coordinate system (top left view corner).

  If we want to translate and then rotate around that *new* origin,
  we need to multiply the transforms the other way around: A*B.

  Three new methods PreTranslateBy(), PreScaleBy() and PreRotateBy()
  implement this. They are later used as a base to add translatation/
  scaling/rotation methods to BView which behave in the expected
  ordering, similar to other graphic APIs.
---
 headers/os/interface/AffineTransform.h | 41 ++++++++++++++++++++++++++
 1 file changed, 41 insertions(+)

diff --git a/headers/os/interface/AffineTransform.h b/headers/os/interface/AffineTransform.h
index b84dee957d3..c296c00c500 100644
--- a/headers/os/interface/AffineTransform.h
+++ b/headers/os/interface/AffineTransform.h
@@ -82,6 +82,8 @@ class BAffineTransform : public BFlattenable {
 	inline	const BAffineTransform&	TranslateBy(double x, double y);
 			const BAffineTransform&	TranslateBy(const BPoint& delta);
 
+	inline	const BAffineTransform&	PreTranslateBy(double x, double y);
+
 			BAffineTransform		TranslateByCopy(double x, double y) const;
 			BAffineTransform		TranslateByCopy(const BPoint& delta) const;
 
@@ -92,6 +94,8 @@ class BAffineTransform : public BFlattenable {
 			const BAffineTransform&	RotateBy(const BPoint& center,
 										double angle);
 
+	inline	const BAffineTransform&	PreRotateBy(double angleRadians);
+
 			BAffineTransform		RotateByCopy(double angle) const;
 			BAffineTransform		RotateByCopy(const BPoint& center,
 										double angle) const;
@@ -109,6 +113,8 @@ class BAffineTransform : public BFlattenable {
 			const BAffineTransform&	ScaleBy(const BPoint& center,
 										const BPoint& scale);
 
+	inline	const BAffineTransform&	PreScaleBy(double x, double y);
+
 			BAffineTransform		ScaleByCopy(double scale) const;
 			BAffineTransform		ScaleByCopy(const BPoint& center,
 										double scale) const;
@@ -244,6 +250,15 @@ BAffineTransform::TranslateBy(double x, double y)
 }
 
 
+inline const BAffineTransform&
+BAffineTransform::PreTranslateBy(double x, double y)
+{
+	tx += x * sx + y * shx;
+	ty += x * shy + y * sy;
+	return *this;
+}
+
+
 inline const BAffineTransform&
 BAffineTransform::RotateBy(double angle)
 {
@@ -262,6 +277,21 @@ BAffineTransform::RotateBy(double angle)
 }
 
 
+inline const BAffineTransform&
+BAffineTransform::PreRotateBy(double angle)
+{
+	double ca = cos(angle);
+	double sa = sin(angle);
+	double newSx = sx * ca + shx * sa;
+	double newSy = -shy * sa + sy * ca;
+	shy = shy * ca + sy * sa;
+	shx = -sx * sa + shx * ca;
+	sx = newSx;
+	sy = newSy;
+	return *this;
+}
+
+
 inline const BAffineTransform&
 BAffineTransform::ScaleBy(double x, double y)
 {
@@ -293,6 +323,17 @@ BAffineTransform::ScaleBy(double s)
 }
 
 
+inline const BAffineTransform&
+BAffineTransform::PreScaleBy(double x, double y)
+{
+	sx *= x;
+	shx *= y;
+	shy *= x;
+	sy *= y;
+	return *this;
+}
+
+
 inline const BAffineTransform&
 BAffineTransform::ShearBy(double x, double y)
 {