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.

3 files changed, 39 insertions, 18 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];
diff --git a/source/blender/editors/space_view3d/view3d_draw.c b/source/blender/editors/space_view3d/view3d_draw.c
index 3a3d5a6683f..a9533b57d8f 100644
--- a/source/blender/editors/space_view3d/view3d_draw.c
+++ b/source/blender/editors/space_view3d/view3d_draw.c
@@ -225,21 +225,21 @@ int ED_view3d_clipping_test(RegionView3D *rv3d, const float vec[3], const int is
 /* ********* end custom clipping *********** */
 
 
-static void drawgrid_draw(ARegion *ar, float wx, float wy, float x, float y, float dx)
+static void drawgrid_draw(ARegion *ar, double wx, double wy, double x, double y, double dx)
 {	
-	float verts[2][2];
+	double verts[2][2];
 
 	x+= (wx); 
 	y+= (wy);
 
 	/* set fixed 'Y' */
 	verts[0][1]= 0.0f;
-	verts[1][1]= (float)ar->winy;
+	verts[1][1]= (double)ar->winy;
 
 	/* iter over 'X' */
-	verts[0][0] = verts[1][0] = x-dx*floorf(x/dx);
+	verts[0][0] = verts[1][0] = x-dx*floor(x/dx);
 	glEnableClientState(GL_VERTEX_ARRAY);
-	glVertexPointer(2, GL_FLOAT, 0, verts);
+	glVertexPointer(2, GL_DOUBLE, 0, verts);
 
 	while (verts[0][0] < ar->winx) {
 		glDrawArrays(GL_LINES, 0, 2);
@@ -248,10 +248,10 @@ static void drawgrid_draw(ARegion *ar, float wx, float wy, float x, float y, flo
 
 	/* set fixed 'X' */
 	verts[0][0]= 0.0f;
-	verts[1][0]= (float)ar->winx;
+	verts[1][0]= (double)ar->winx;
 
 	/* iter over 'Y' */
-	verts[0][1]= verts[1][1]= y-dx*floorf(y/dx);
+	verts[0][1]= verts[1][1]= y-dx*floor(y/dx);
 	while (verts[0][1] < ar->winy) {
 		glDrawArrays(GL_LINES, 0, 2);
 		verts[0][1] = verts[1][1] = verts[0][1] + dx;
@@ -266,16 +266,13 @@ static void drawgrid(UnitSettings *unit, ARegion *ar, View3D *v3d, const char **
 {
 	/* extern short bgpicmode; */
 	RegionView3D *rv3d= ar->regiondata;
-	float wx, wy, x, y, fw, fx, fy, dx;
-	float vec4[4];
+	double wx, wy, x, y, fw, fx, fy, dx;
+	double vec4[4];
 	unsigned char col[3], col2[3];
 
-	vec4[0]=vec4[1]=vec4[2]=0.0; 
-	vec4[3]= 1.0;
-	mul_m4_v4(rv3d->persmat, vec4);
-	fx= vec4[0]; 
-	fy= vec4[1]; 
-	fw= vec4[3];
+	fx= rv3d->persmat[3][0];
+	fy= rv3d->persmat[3][1];
+	fw= rv3d->persmat[3][3];
 
 	wx= (ar->winx/2.0);	/* because of rounding errors, grid at wrong location */
 	wy= (ar->winy/2.0);
@@ -287,7 +284,7 @@ static void drawgrid(UnitSettings *unit, ARegion *ar, View3D *v3d, const char **
 
 	vec4[2]= 0.0;
 	vec4[3]= 1.0;
-	mul_m4_v4(rv3d->persmat, vec4);
+	mul_m4_v4d(rv3d->persmat, vec4);
 	fx= vec4[0]; 
 	fy= vec4[1]; 
 	fw= vec4[3];
@@ -305,7 +302,7 @@ static void drawgrid(UnitSettings *unit, ARegion *ar, View3D *v3d, const char **
 		 * items are less useful when dealing with units */
 		void *usys;
 		int len, i;
-		float dx_scalar;
+		double dx_scalar;
 		float blend_fac;
 
 		bUnit_GetSystem(&usys, &len, unit->system, B_UNIT_LENGTH);
@@ -313,7 +310,7 @@ static void drawgrid(UnitSettings *unit, ARegion *ar, View3D *v3d, const char **
 		if (usys) {
 			i= len;
 			while (i--) {
-				float scalar= bUnit_GetScaler(usys, i);
+				double scalar= bUnit_GetScaler(usys, i);
 
 				dx_scalar = dx * scalar / unit->scale_length;
 				if (dx_scalar < (GRID_MIN_PX*2))