From 157fbc60ea4cea577b4e5e0e38f0dd56acd7d01c Mon Sep 17 00:00:00 2001
From: Lateasusual <chris@lateasusual.com>
Date: Thu, 20 Apr 2023 19:54:58 +0100
Subject: [PATCH] WIP: Alternative trackball rotation proposal

---
 .../editors/transform/transform_data.h        |  3 ++
 .../transform/transform_mode_trackball.c      | 34 +++++++++++++++++++
 2 files changed, 37 insertions(+)

diff --git a/source/blender/editors/transform/transform_data.h b/source/blender/editors/transform/transform_data.h
index 2518fef3b39..78d55111004 100644
--- a/source/blender/editors/transform/transform_data.h
+++ b/source/blender/editors/transform/transform_data.h
@@ -133,6 +133,9 @@ typedef struct TransData {
   TransDataCurveHandleFlags *hdata;
   /** If set, copy of Object or #bPoseChannel protection. */
   short protectflag;
+  // Local rotation accumulator
+  short rotmtx_init;
+  float rotmtx[3][3];
 } TransData;
 
 #define TRANSDATA_THREAD_LIMIT 1024
diff --git a/source/blender/editors/transform/transform_mode_trackball.c b/source/blender/editors/transform/transform_mode_trackball.c
index 3716826800b..587f06fa2e3 100644
--- a/source/blender/editors/transform/transform_mode_trackball.c
+++ b/source/blender/editors/transform/transform_mode_trackball.c
@@ -51,7 +51,24 @@ static void transdata_elem_trackball(const TransInfo *t,
   float mat_buf[3][3];
   const float(*mat)[3] = mat_final;
   if (t->flag & T_PROP_EDIT) {
+#if 0
+    float angle_temp;
+    float axis_temp[3];
+
+    mat3_to_axis_angle(axis_temp, &angle_temp, mat_final);
+
+    axis_angle_normalized_to_mat3(mat_buf, axis_temp, angle_temp *= td->factor);
+#else
+    if (UNLIKELY(!td->rotmtx_init)) {
+      unit_m3(td->rotmtx);
+      td->rotmtx_init = 1;
+    }
     axis_angle_normalized_to_mat3(mat_buf, axis, td->factor * angle);
+
+    mul_m3_m3_post(mat_buf, td->rotmtx);
+
+    copy_m3_m3(td->rotmtx, mat_buf);
+#endif
     mat = mat_buf;
   }
   ElementRotation(t, tc, td, mat, t->around);
@@ -94,8 +111,16 @@ static void applyTrackballValue(TransInfo *t, const float axis[3], const float a
   float mat_final[3][3];
   int i;
 
+  // Temp hack since I don't have anywhere better to store this
+  //  - these aren't used for trackball rotations anyway
+  float (*mat_temp)[3] = t->orient[0].matrix;
+
   axis_angle_normalized_to_mat3(mat_final, axis, angle);
 
+  // Combine delta rotation with stored matrix
+  mul_m3_m3_post(mat_final, mat_temp);
+  copy_m3_m3(mat_temp, mat_final);
+
   FOREACH_TRANS_DATA_CONTAINER (t, tc) {
     if (tc->data_len < TRANSDATA_THREAD_LIMIT) {
       TransData *td = tc->data;
@@ -128,7 +153,13 @@ static void applyTrackball(TransInfo *t, const int UNUSED(mval[2]))
   size_t ofs = 0;
   float phi[2];
 
+  // Temp hack since I'm not sure where is best to store temporary data like this
+  float* phi_prev = t->values + 2;
+
+  // Get delta phi, and write back resulting phi value
   copy_v2_v2(phi, t->values);
+  sub_v2_v2(phi, phi_prev);
+  copy_v2_v2(phi_prev, t->values);
 
   transform_snap_increment(t, phi);
 
@@ -194,6 +225,9 @@ void initTrackball(TransInfo *t)
 
   initMouseInputMode(t, &t->mouse, INPUT_TRACKBALL);
 
+  // TEMP HACK
+  unit_m3(t->orient[0].matrix);
+
   t->idx_max = 1;
   t->num.idx_max = 1;
   t->snap[0] = DEG2RAD(5.0);
-- 
2.30.2