Fix ##30455: Orthographic grid alignment jumps/shifts when zooming

Issue was caused by precision errors with floats.
Made internal grid drawing stuff using doubles and also added some
functions to multiply double vector by float matrix which also makes
all intermediate calculation in doubles.

2 files changed, 24 insertions, 0 deletions

diff --git a/source/blender/blenlib/BLI_math_matrix.h b/source/blender/blenlib/BLI_math_matrix.h
index 328b5614f52..de4bd203eb6 100644
--- a/source/blender/blenlib/BLI_math_matrix.h
+++ b/source/blender/blenlib/BLI_math_matrix.h
@@ -103,6 +103,11 @@ int invert_m3_m3(float R[3][3], float A[3][3]);
 int invert_m4(float R[4][4]);
 int invert_m4_m4(float R[4][4], float A[4][4]);
 
+/* double ariphmetics */
+void mul_m4_v4d(float M[4][4], double r[4]);
+void mul_v4d_m4v4d(double r[4], float M[4][4], double v[4]);
+
+
 /****************************** Linear Algebra *******************************/
 
 void transpose_m3(float R[3][3]);
diff --git a/source/blender/blenlib/intern/math_matrix.c b/source/blender/blenlib/intern/math_matrix.c
index 69e4102b497..b777b394005 100644
--- a/source/blender/blenlib/intern/math_matrix.c
+++ b/source/blender/blenlib/intern/math_matrix.c
@@ -373,6 +373,25 @@ void mul_m4_v4(float mat[4][4], float r[4])
 	mul_v4_m4v4(r, mat, r);
 }
 
+void mul_v4d_m4v4d(double r[4], float mat[4][4], double v[4])
+{
+	double x, y, z;
+
+	x= v[0];
+	y= v[1];
+	z= v[2];
+
+	r[0]= x*(double)mat[0][0] + y*(double)mat[1][0] + z*(double)mat[2][0] + (double)mat[3][0]*v[3];
+	r[1]= x*(double)mat[0][1] + y*(double)mat[1][1] + z*(double)mat[2][1] + (double)mat[3][1]*v[3];
+	r[2]= x*(double)mat[0][2] + y*(double)mat[1][2] + z*(double)mat[2][2] + (double)mat[3][2]*v[3];
+	r[3]= x*(double)mat[0][3] + y*(double)mat[1][3] + z*(double)mat[2][3] + (double)mat[3][3]*v[3];
+}
+
+void mul_m4_v4d(float mat[4][4], double r[4])
+{
+	mul_v4d_m4v4d(r, mat, r);
+}
+
 void mul_v3_m3v3(float r[3], float M[3][3], float a[3])
 {
 	r[0]= M[0][0]*a[0] + M[1][0]*a[1] + M[2][0]*a[2];