From cabaee680e66651f2a9a6e72996e9f21d47c274f Mon Sep 17 00:00:00 2001
From: Jacek Olszak <jacekolszak@gmail.com>
Date: Tue, 12 Feb 2019 14:57:03 +0100
Subject: [PATCH] #159 Fix unproject for rotated matrix
---
geometry.go | 12 +++++-------
geometry_test.go | 29 +++++++++++++++++++++++++++++
2 files changed, 34 insertions(+), 7 deletions(-)
diff --git a/geometry.go b/geometry.go
index 72d148e..621a0b4 100644
--- a/geometry.go
+++ b/geometry.go
@@ -401,13 +401,11 @@ func (m Matrix) Project(u Vec) Vec {
// Unproject does the inverse operation to Project.
//
-// It turns out that multiplying a vector by the inverse matrix of m can be nearly-accomplished by
-// subtracting the translate part of the matrix and multplying by the inverse of the top-left 2x2
-// matrix, and the inverse of a 2x2 matrix is simple enough to just be inlined in the computation.
-//
// Time complexity is O(1).
func (m Matrix) Unproject(u Vec) Vec {
- d := (m[0] * m[3]) - (m[1] * m[2])
- u.X, u.Y = (u.X-m[4])/d, (u.Y-m[5])/d
- return Vec{u.X*m[3] - u.Y*m[1], u.Y*m[0] - u.X*m[2]}
+ det := m[0]*m[3] - m[2]*m[1]
+ return Vec{
+ m[3]/det*u.X - m[2]/det*u.Y + m[2]*m[5] - m[3]*m[4],
+ -m[1]/det*u.X + m[0]/det*u.Y + m[1]*m[4] - m[0]*m[5],
+ }
}
diff --git a/geometry_test.go b/geometry_test.go
index e1c1a6f..f97b8cd 100644
--- a/geometry_test.go
+++ b/geometry_test.go
@@ -2,6 +2,8 @@ package pixel_test
import (
"fmt"
+ "github.com/stretchr/testify/assert"
+ "math"
"testing"
"github.com/faiface/pixel"
@@ -77,3 +79,30 @@ func TestResizeRect(t *testing.T) {
})
}
}
+
+func TestMatrix_Unproject(t *testing.T) {
+ t.Run("for rotated matrix", func(t *testing.T) {
+ matrix := pixel.IM.Rotated(pixel.ZV, math.Pi/2)
+ unprojected := matrix.Unproject(pixel.V(0, 1))
+ assert.InDelta(t, unprojected.X, 1, 0.01)
+ assert.InDelta(t, unprojected.Y, 0, 0.01)
+ })
+ t.Run("for moved matrix", func(t *testing.T) {
+ matrix := pixel.IM.Moved(pixel.V(5, 5))
+ unprojected := matrix.Unproject(pixel.V(0, 0))
+ assert.InDelta(t, unprojected.X, -5, 0.01)
+ assert.InDelta(t, unprojected.Y, -5, 0.01)
+ })
+ t.Run("for scaled matrix", func(t *testing.T) {
+ matrix := pixel.IM.Scaled(pixel.ZV, 2)
+ unprojected := matrix.Unproject(pixel.V(4, 4))
+ assert.InDelta(t, unprojected.X, 2, 0.01)
+ assert.InDelta(t, unprojected.Y, 2, 0.01)
+ })
+ t.Run("for singular matrix", func(t *testing.T) {
+ matrix := pixel.Matrix{0, 0, 0, 0, 0, 0}
+ unprojected := matrix.Unproject(pixel.ZV)
+ assert.True(t, math.IsNaN(unprojected.X))
+ assert.True(t, math.IsNaN(unprojected.Y))
+ })
+}
--
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