From 0b1221c813ef3ae83bb8279aca15d018c68305da Mon Sep 17 00:00:00 2001
From: Marcelo Mutzbauer <1xundoredo@gmail.com>
Date: Mon, 25 Dec 2023 18:33:03 +0100
Subject: [PATCH 1/6] Fix #116418

---
 source/blender/editors/sculpt_paint/sculpt.cc | 42 ++++++++++++-------
 1 file changed, 26 insertions(+), 16 deletions(-)

diff --git a/source/blender/editors/sculpt_paint/sculpt.cc b/source/blender/editors/sculpt_paint/sculpt.cc
index e2a0d3ad9e1..fc7e139ef7f 100644
--- a/source/blender/editors/sculpt_paint/sculpt.cc
+++ b/source/blender/editors/sculpt_paint/sculpt.cc
@@ -2739,20 +2739,22 @@ static void update_sculpt_normal(Sculpt *sd, Object *ob, Span<PBVHNode *> nodes)
   }
 }
 
-static void calc_local_y(ViewContext *vc, const float center[3], float y[3])
+static void calc_local_from_screen(ViewContext *vc,
+                                   const float center[3],
+                                   const float screen_dir[2],
+                                   float r_local_dir[3])
 {
   Object *ob = vc->obact;
   float loc[3];
-  const float xy_delta[2] = {0.0f, 1.0f};
 
-  mul_v3_m4v3(loc, ob->world_to_object, center);
+  mul_v3_m4v3(loc, ob->object_to_world, center);
   const float zfac = ED_view3d_calc_zfac(vc->rv3d, loc);
 
-  ED_view3d_win_to_delta(vc->region, xy_delta, zfac, y);
-  normalize_v3(y);
+  ED_view3d_win_to_delta(vc->region, screen_dir, zfac, r_local_dir);
+  normalize_v3(r_local_dir);
 
-  add_v3_v3(y, ob->loc);
-  mul_m4_v3(ob->world_to_object, y);
+  add_v3_v3(r_local_dir, ob->loc);
+  mul_m4_v3(ob->world_to_object, r_local_dir);
 }
 
 static void calc_brush_local_mat(const float rotation,
@@ -2765,7 +2767,6 @@ static void calc_brush_local_mat(const float rotation,
   float mat[4][4];
   float scale[4][4];
   float angle, v[3];
-  float up[3];
 
   /* Ensure `ob->world_to_object` is up to date. */
   invert_m4_m4(ob->world_to_object, ob->object_to_world);
@@ -2776,17 +2777,26 @@ static void calc_brush_local_mat(const float rotation,
   mat[2][3] = 0.0f;
   mat[3][3] = 1.0f;
 
-  /* Get view's up vector in object-space. */
-  calc_local_y(cache->vc, cache->location, up);
-
-  /* Calculate the X axis of the local matrix. */
-  cross_v3_v3v3(v, up, cache->sculpt_normal);
-  /* Apply rotation (user angle, rake, etc.) to X axis. */
+  /* Read rotation (user angle, rake, etc.) to find the view's transverse direction. */
   angle = rotation - cache->special_rotation;
-  rotate_v3_v3v3fl(mat[0], v, cache->sculpt_normal, angle);
+  float transverse_view[2];
+  float transverse_local[3];
+  transverse_view[0] = cosf(angle);
+  transverse_view[1] = sinf(angle);
+  /* Convert view's brush transverse drection to object-space */
+  calc_local_from_screen(cache->vc, cache->location, transverse_view, transverse_local);
+
+  /* Calculate the movement direction for the local matrix.
+   * Note that there is a deliberate prioritization here: Our calculations are
+   * designed such that the _motion vector_ gets projected into the tangent space;
+   * in most cases this will be more intuitive than projecting the transverse
+   * direction (which is orthogonal to the motion direction and therefore less
+   * apparent to the user). */
+  cross_v3_v3v3(v, transverse_local, cache->sculpt_normal);
+  normalize_v3_v3(mat[1], v);
 
   /* Get other axes. */
-  cross_v3_v3v3(mat[1], cache->sculpt_normal, mat[0]);
+  cross_v3_v3v3(mat[0], mat[1], cache->sculpt_normal);
   copy_v3_v3(mat[2], cache->sculpt_normal);
 
   /* Set location. */
-- 
2.30.2


From 58287ec640f581d79b6e1a6cfdf922783ab9bb0f Mon Sep 17 00:00:00 2001
From: Marcelo Mutzbauer <1xundoredo@gmail.com>
Date: Mon, 25 Dec 2023 18:56:48 +0100
Subject: [PATCH 2/6] Minor rearrangements

---
 source/blender/editors/sculpt_paint/sculpt.cc | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/source/blender/editors/sculpt_paint/sculpt.cc b/source/blender/editors/sculpt_paint/sculpt.cc
index fc7e139ef7f..7660b998502 100644
--- a/source/blender/editors/sculpt_paint/sculpt.cc
+++ b/source/blender/editors/sculpt_paint/sculpt.cc
@@ -2780,10 +2780,10 @@ static void calc_brush_local_mat(const float rotation,
   /* Read rotation (user angle, rake, etc.) to find the view's transverse direction. */
   angle = rotation - cache->special_rotation;
   float transverse_view[2];
-  float transverse_local[3];
   transverse_view[0] = cosf(angle);
   transverse_view[1] = sinf(angle);
   /* Convert view's brush transverse drection to object-space */
+  float transverse_local[3];
   calc_local_from_screen(cache->vc, cache->location, transverse_view, transverse_local);
 
   /* Calculate the movement direction for the local matrix.
-- 
2.30.2


From 86c6ee962425435826b2eaacd9597876ac85ae98 Mon Sep 17 00:00:00 2001
From: Marcelo Mutzbauer <1xundoredo@gmail.com>
Date: Mon, 25 Dec 2023 23:10:39 +0100
Subject: [PATCH 3/6] More intuitive(?) measurement of the rotation angle

---
 source/blender/blenkernel/intern/paint.cc     |  4 ++--
 source/blender/editors/sculpt_paint/sculpt.cc | 24 +++++++++++--------
 2 files changed, 16 insertions(+), 12 deletions(-)

diff --git a/source/blender/blenkernel/intern/paint.cc b/source/blender/blenkernel/intern/paint.cc
index aea34a2000b..9edc615aa27 100644
--- a/source/blender/blenkernel/intern/paint.cc
+++ b/source/blender/blenkernel/intern/paint.cc
@@ -1352,11 +1352,11 @@ bool paint_calculate_rake_rotation(UnifiedPaintSettings *ups,
     }
 
     float dpos[2];
-    sub_v2_v2v2(dpos, ups->last_rake, mouse_pos);
+    sub_v2_v2v2(dpos, mouse_pos, ups->last_rake);
 
     /* Limit how often we update the angle to prevent jitter. */
     if (len_squared_v2(dpos) >= r * r) {
-      rotation = atan2f(dpos[0], dpos[1]);
+      rotation = atan2f(dpos[1], dpos[0]);
 
       copy_v2_v2(ups->last_rake, mouse_pos);
 
diff --git a/source/blender/editors/sculpt_paint/sculpt.cc b/source/blender/editors/sculpt_paint/sculpt.cc
index 7660b998502..7c1379ccaaa 100644
--- a/source/blender/editors/sculpt_paint/sculpt.cc
+++ b/source/blender/editors/sculpt_paint/sculpt.cc
@@ -2777,22 +2777,26 @@ static void calc_brush_local_mat(const float rotation,
   mat[2][3] = 0.0f;
   mat[3][3] = 1.0f;
 
-  /* Read rotation (user angle, rake, etc.) to find the view's transverse direction. */
-  angle = rotation - cache->special_rotation;
-  float transverse_view[2];
-  transverse_view[0] = cosf(angle);
-  transverse_view[1] = sinf(angle);
-  /* Convert view's brush transverse drection to object-space */
-  float transverse_local[3];
-  calc_local_from_screen(cache->vc, cache->location, transverse_view, transverse_local);
+  /* Read rotation (user angle, rake, etc.) to find the view's movement direction. */
+  angle = rotation + cache->special_rotation;
+  float normal_screen[2];
+  normal_screen[0] = -sinf(angle);
+  normal_screen[1] = cosf(angle);
+  /* Convert view's brush transverse direction to object-space,
+   * i.e. the normal of the plane described by the motion */
+  float normal_local[3];
+  calc_local_from_screen(cache->vc, cache->location, normal_screen, normal_local);
 
   /* Calculate the movement direction for the local matrix.
    * Note that there is a deliberate prioritization here: Our calculations are
    * designed such that the _motion vector_ gets projected into the tangent space;
    * in most cases this will be more intuitive than projecting the transverse
    * direction (which is orthogonal to the motion direction and therefore less
-   * apparent to the user). */
-  cross_v3_v3v3(v, transverse_local, cache->sculpt_normal);
+   * apparent to the user).
+   * The Y-axis of the brush-local frame has to lie in the intersection of the tangent plane
+   * and the motion plane. */
+
+  cross_v3_v3v3(v, normal_local, cache->sculpt_normal);
   normalize_v3_v3(mat[1], v);
 
   /* Get other axes. */
-- 
2.30.2


From 04906729be38d62ea478e36dc3491c2ba495475e Mon Sep 17 00:00:00 2001
From: Marcelo Mutzbauer <1xundoredo@gmail.com>
Date: Mon, 25 Dec 2023 23:19:56 +0100
Subject: [PATCH 4/6] Better naming

---
 source/blender/editors/sculpt_paint/sculpt.cc | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/source/blender/editors/sculpt_paint/sculpt.cc b/source/blender/editors/sculpt_paint/sculpt.cc
index 7c1379ccaaa..128c54b5092 100644
--- a/source/blender/editors/sculpt_paint/sculpt.cc
+++ b/source/blender/editors/sculpt_paint/sculpt.cc
@@ -2779,13 +2779,13 @@ static void calc_brush_local_mat(const float rotation,
 
   /* Read rotation (user angle, rake, etc.) to find the view's movement direction. */
   angle = rotation + cache->special_rotation;
-  float normal_screen[2];
-  normal_screen[0] = -sinf(angle);
-  normal_screen[1] = cosf(angle);
+  float motion_normal_screen[2];
+  motion_normal_screen[0] = -sinf(angle);
+  motion_normal_screen[1] = cosf(angle);
   /* Convert view's brush transverse direction to object-space,
    * i.e. the normal of the plane described by the motion */
-  float normal_local[3];
-  calc_local_from_screen(cache->vc, cache->location, normal_screen, normal_local);
+  float motion_normal_local[3];
+  calc_local_from_screen(cache->vc, cache->location, motion_normal_screen, motion_normal_local);
 
   /* Calculate the movement direction for the local matrix.
    * Note that there is a deliberate prioritization here: Our calculations are
@@ -2796,7 +2796,7 @@ static void calc_brush_local_mat(const float rotation,
    * The Y-axis of the brush-local frame has to lie in the intersection of the tangent plane
    * and the motion plane. */
 
-  cross_v3_v3v3(v, normal_local, cache->sculpt_normal);
+  cross_v3_v3v3(v, motion_normal_local, cache->sculpt_normal);
   normalize_v3_v3(mat[1], v);
 
   /* Get other axes. */
-- 
2.30.2


From 1ae70f82ee3edbb08de5425bd860868a4bd647c3 Mon Sep 17 00:00:00 2001
From: Marcelo Mutzbauer <1xundoredo@gmail.com>
Date: Tue, 2 Jan 2024 18:23:43 +0100
Subject: [PATCH 5/6] Fix some rotation problems

---
 source/blender/blenkernel/intern/brush.cc           |  3 ++-
 source/blender/blenkernel/intern/paint.cc           |  2 +-
 source/blender/editors/sculpt_paint/paint_cursor.cc |  2 +-
 source/blender/editors/sculpt_paint/paint_stroke.cc |  6 +++---
 source/blender/editors/sculpt_paint/sculpt.cc       | 11 +++++++----
 source/blender/makesdna/DNA_scene_types.h           |  3 +++
 6 files changed, 17 insertions(+), 10 deletions(-)

diff --git a/source/blender/blenkernel/intern/brush.cc b/source/blender/blenkernel/intern/brush.cc
index a070a6731c9..685b8f05625 100644
--- a/source/blender/blenkernel/intern/brush.cc
+++ b/source/blender/blenkernel/intern/brush.cc
@@ -2149,7 +2149,8 @@ float BKE_brush_sample_tex_3d(const Scene *scene,
      * the texture is not rotated by skipping the calls to
      * atan2, sqrtf, sin, and cos. */
     if (rotation > 0.001f || rotation < -0.001f) {
-      const float angle = atan2f(y, x) + rotation;
+      /* Since we are sampling, rotation must be negated */
+      const float angle = atan2f(y, x) - rotation;
       const float flen = sqrtf(x * x + y * y);
 
       x = flen * cosf(angle);
diff --git a/source/blender/blenkernel/intern/paint.cc b/source/blender/blenkernel/intern/paint.cc
index 9edc615aa27..1038bae53de 100644
--- a/source/blender/blenkernel/intern/paint.cc
+++ b/source/blender/blenkernel/intern/paint.cc
@@ -1356,7 +1356,7 @@ bool paint_calculate_rake_rotation(UnifiedPaintSettings *ups,
 
     /* Limit how often we update the angle to prevent jitter. */
     if (len_squared_v2(dpos) >= r * r) {
-      rotation = atan2f(dpos[1], dpos[0]);
+      rotation = atan2f(dpos[1], dpos[0]) + float(0.5f * M_PI);
 
       copy_v2_v2(ups->last_rake, mouse_pos);
 
diff --git a/source/blender/editors/sculpt_paint/paint_cursor.cc b/source/blender/editors/sculpt_paint/paint_cursor.cc
index dbd516654ff..7dd85358623 100644
--- a/source/blender/editors/sculpt_paint/paint_cursor.cc
+++ b/source/blender/editors/sculpt_paint/paint_cursor.cc
@@ -584,7 +584,7 @@ static bool paint_draw_tex_overlay(UnifiedPaintSettings *ups,
 
       /* Brush rotation. */
       GPU_matrix_translate_2fv(center);
-      GPU_matrix_rotate_2d(-RAD2DEGF(primary ? ups->brush_rotation : ups->brush_rotation_sec));
+      GPU_matrix_rotate_2d(RAD2DEGF(primary ? ups->brush_rotation : ups->brush_rotation_sec));
       GPU_matrix_translate_2f(-center[0], -center[1]);
 
       /* Scale based on tablet pressure. */
diff --git a/source/blender/editors/sculpt_paint/paint_stroke.cc b/source/blender/editors/sculpt_paint/paint_stroke.cc
index 1fd84646b6f..0c6c5010d83 100644
--- a/source/blender/editors/sculpt_paint/paint_stroke.cc
+++ b/source/blender/editors/sculpt_paint/paint_stroke.cc
@@ -46,7 +46,7 @@
 #include "paint_intern.hh"
 #include "sculpt_intern.hh"
 
-//#define DEBUG_TIME
+// #define DEBUG_TIME
 
 #ifdef DEBUG_TIME
 #  include "PIL_time_utildefines.h"
@@ -399,7 +399,7 @@ static bool paint_brush_update(bContext *C,
 
     ups->anchored_size = ups->pixel_radius = sqrtf(dx * dx + dy * dy);
 
-    ups->brush_rotation = ups->brush_rotation_sec = atan2f(dx, dy) + float(M_PI);
+    ups->brush_rotation = ups->brush_rotation_sec = atan2f(dy, dx) + float(0.5f * M_PI);
 
     if (brush->flag & BRUSH_EDGE_TO_EDGE) {
       halfway[0] = dx * 0.5f + stroke->initial_mouse[0];
@@ -1372,7 +1372,7 @@ static bool paint_stroke_curve_end(bContext *C, wmOperator *op, PaintStroke *str
 
       for (j = 0; j < PAINT_CURVE_NUM_SEGMENTS; j++) {
         if (do_rake) {
-          float rotation = atan2f(tangents[2 * j], tangents[2 * j + 1]);
+          float rotation = atan2f(tangents[2 * j + 1], tangents[2 * j]) + float(0.5f * M_PI);
           paint_update_brush_rake_rotation(ups, br, rotation);
         }
 
diff --git a/source/blender/editors/sculpt_paint/sculpt.cc b/source/blender/editors/sculpt_paint/sculpt.cc
index 128c54b5092..c209c3a0a92 100644
--- a/source/blender/editors/sculpt_paint/sculpt.cc
+++ b/source/blender/editors/sculpt_paint/sculpt.cc
@@ -2777,11 +2777,14 @@ static void calc_brush_local_mat(const float rotation,
   mat[2][3] = 0.0f;
   mat[3][3] = 1.0f;
 
-  /* Read rotation (user angle, rake, etc.) to find the view's movement direction. */
+  /* Read rotation (user angle, rake, etc.) to find the view's movement direction (negative X of
+   * the brush). */
   angle = rotation + cache->special_rotation;
+  /* By convention, motion direction points down the brush's Y axis, the angle represents the X
+   * axis, normal is a 90 deg ccw rotation of the motion direction. */
   float motion_normal_screen[2];
-  motion_normal_screen[0] = -sinf(angle);
-  motion_normal_screen[1] = cosf(angle);
+  motion_normal_screen[0] = cosf(angle);
+  motion_normal_screen[1] = sinf(angle);
   /* Convert view's brush transverse direction to object-space,
    * i.e. the normal of the plane described by the motion */
   float motion_normal_local[3];
@@ -2796,7 +2799,7 @@ static void calc_brush_local_mat(const float rotation,
    * The Y-axis of the brush-local frame has to lie in the intersection of the tangent plane
    * and the motion plane. */
 
-  cross_v3_v3v3(v, motion_normal_local, cache->sculpt_normal);
+  cross_v3_v3v3(v, cache->sculpt_normal, motion_normal_local);
   normalize_v3_v3(mat[1], v);
 
   /* Get other axes. */
diff --git a/source/blender/makesdna/DNA_scene_types.h b/source/blender/makesdna/DNA_scene_types.h
index effad7d3116..6f99a40d51a 100644
--- a/source/blender/makesdna/DNA_scene_types.h
+++ b/source/blender/makesdna/DNA_scene_types.h
@@ -1351,6 +1351,9 @@ typedef struct UnifiedPaintSettings {
   float average_stroke_accum[3];
   int average_stroke_counter;
 
+  /* How much brush should be rotated in the view plane, 0 means x points right, y points up.
+   * The convention is that the brush's _negative_ Y axis points in the tangent direction (of the
+   * mouse curve, Bezier curve, etc.) */
   float brush_rotation;
   float brush_rotation_sec;
 
-- 
2.30.2


From caf44e3c624fe300c78221b4ac95e2a4be706a8c Mon Sep 17 00:00:00 2001
From: Marcelo Mutzbauer <1xundoredo@gmail.com>
Date: Wed, 3 Jan 2024 15:34:14 +0100
Subject: [PATCH 6/6] Forgot to add a file in my previous commit

---
 source/blender/blenkernel/intern/brush.cc | 11 +++++------
 1 file changed, 5 insertions(+), 6 deletions(-)

diff --git a/source/blender/blenkernel/intern/brush.cc b/source/blender/blenkernel/intern/brush.cc
index 685b8f05625..5c146316f27 100644
--- a/source/blender/blenkernel/intern/brush.cc
+++ b/source/blender/blenkernel/intern/brush.cc
@@ -2116,7 +2116,7 @@ float BKE_brush_sample_tex_3d(const Scene *scene,
     if (mtex->brush_map_mode == MTEX_MAP_MODE_VIEW) {
       /* keep coordinates relative to mouse */
 
-      rotation += ups->brush_rotation;
+      rotation -= ups->brush_rotation;
 
       x = point_2d[0] - ups->tex_mouse[0];
       y = point_2d[1] - ups->tex_mouse[1];
@@ -2134,7 +2134,7 @@ float BKE_brush_sample_tex_3d(const Scene *scene,
       y = point_2d[1];
     }
     else if (mtex->brush_map_mode == MTEX_MAP_MODE_RANDOM) {
-      rotation += ups->brush_rotation;
+      rotation -= ups->brush_rotation;
       /* these contain a random coordinate */
       x = point_2d[0] - ups->tex_mouse[0];
       y = point_2d[1] - ups->tex_mouse[1];
@@ -2149,8 +2149,7 @@ float BKE_brush_sample_tex_3d(const Scene *scene,
      * the texture is not rotated by skipping the calls to
      * atan2, sqrtf, sin, and cos. */
     if (rotation > 0.001f || rotation < -0.001f) {
-      /* Since we are sampling, rotation must be negated */
-      const float angle = atan2f(y, x) - rotation;
+      const float angle = atan2f(y, x) + rotation;
       const float flen = sqrtf(x * x + y * y);
 
       x = flen * cosf(angle);
@@ -2230,7 +2229,7 @@ float BKE_brush_sample_masktex(
     if (mtex->brush_map_mode == MTEX_MAP_MODE_VIEW) {
       /* keep coordinates relative to mouse */
 
-      rotation += ups->brush_rotation_sec;
+      rotation -= ups->brush_rotation_sec;
 
       x = point_2d[0] - ups->mask_tex_mouse[0];
       y = point_2d[1] - ups->mask_tex_mouse[1];
@@ -2248,7 +2247,7 @@ float BKE_brush_sample_masktex(
       y = point_2d[1];
     }
     else if (mtex->brush_map_mode == MTEX_MAP_MODE_RANDOM) {
-      rotation += ups->brush_rotation_sec;
+      rotation -= ups->brush_rotation_sec;
       /* these contain a random coordinate */
       x = point_2d[0] - ups->mask_tex_mouse[0];
       y = point_2d[1] - ups->mask_tex_mouse[1];
-- 
2.30.2