GooEngine: Add Continous Trackball mode option

scripts/startup/bl_ui/space_userpref.py

@@ -1700,6 +1700,7 @@ class USERPREF_PT_input_mouse(InputPanel, CenterAlignMixIn, Panel):
             subrow.active = inputs.use_mouse_emulate_3_button
 
         flow.prop(inputs, "use_mouse_continuous")
+        flow.prop(inputs, "use_accumulative_trackball")
         flow.prop(inputs, "use_drag_immediately")
         flow.prop(inputs, "mouse_double_click_time", text="Double Click Speed")
         flow.prop(inputs, "drag_threshold_mouse")

source/blender/blenloader/intern/versioning_userdef.cc

@@ -723,7 +723,7 @@ void blo_do_versions_userdef(UserDef *userdef)
       userdef->pixelsize = 1.0f;
     }
     /* Clear old userdef flag for "Camera Parent Lock". */
-    userdef->uiflag &= ~USER_UIFLAG_UNUSED_3;
+    userdef->uiflag &= ~USER_ACCUMULATE_TRACKBALL;
   }
 
   if (!USER_VERSION_ATLEAST(292, 9)) {

source/blender/editors/transform/transform_data.hh

@@ -136,6 +136,9 @@ struct TransData {
   TransDataCurveHandleFlags *hdata;
   /** If set, copy of Object or #bPoseChannel protection. */
   short protectflag;
+  /** Local rotation accumulator for Trackball (is initialized) */
+  short rotmtx_init;
+  float rotmtx[3][3];
 };
 
 #define TRANSDATA_THREAD_LIMIT 1024

source/blender/editors/transform/transform_mode_trackball.cc

@@ -54,7 +54,18 @@ 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 (UNLIKELY(!td->rotmtx_init)) {
+      unit_m3(td->rotmtx);
+      td->rotmtx_init = true;
+    }
     axis_angle_normalized_to_mat3(mat_buf, axis, td->factor * angle);
+
+    /* Apply "continuous" trackball rotation. */
+    if (U.uiflag & USER_ACCUMULATE_TRACKBALL) {
+      mul_m3_m3_post(mat_buf, td->rotmtx);
+      copy_m3_m3(td->rotmtx, mat_buf);
+    }
+
     mat = mat_buf;
   }
   ElementRotation(t, tc, td, mat, t->around);
@@ -97,8 +108,16 @@ static void applyTrackballValue(TransInfo *t, const float axis[3], const float a
   float mat_final[3][3];
   int i;
 
+  /* Hack: Use otherwise-unused matrix storage for this */
+  float (*mat_temp)[3] = t->orient[0].matrix;
+
   axis_angle_normalized_to_mat3(mat_final, axis, angle);
 
+  if (U.uiflag & USER_ACCUMULATE_TRACKBALL) {
+    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;
@@ -130,8 +149,17 @@ static void applyTrackball(TransInfo *t)
   size_t ofs = 0;
   float phi[2];
 
+  /* Store previous mouse coordinates as (z,w) in the xyzw vector */
+  float* phi_prev = t->values + 2;
+
   copy_v2_v2(phi, t->values);
 
+  /* Get mouse delta only since phi_prev */
+  if (U.uiflag & USER_ACCUMULATE_TRACKBALL) {
+    sub_v2_v2(phi, phi_prev);
+    copy_v2_v2(phi_prev, t->values);
+  }
+
   transform_snap_increment(t, phi);
 
   applyNumInput(&t->num, phi);
@@ -194,6 +222,9 @@ static void initTrackball(TransInfo *t, wmOperator * /*op*/)
 
   initMouseInputMode(t, &t->mouse, INPUT_TRACKBALL);
 
+  /* Initialize re-used matrix storage to I */
+  unit_m3(t->orient[0].matrix);
+
   t->idx_max = 1;
   t->num.idx_max = 1;
   t->snap[0] = DEG2RAD(5.0);

source/blender/makesdna/DNA_userdef_types.h

@@ -1192,7 +1192,7 @@ typedef enum eUserpref_UI_Flag {
   USER_HIDE_DOT = (1 << 16),
   USER_SHOW_GIZMO_NAVIGATE = (1 << 17),
   USER_SHOW_VIEWPORTNAME = (1 << 18),
-  USER_UIFLAG_UNUSED_3 = (1 << 19), /* Cleared. */
+  USER_ACCUMULATE_TRACKBALL = (1 << 19),
   USER_ZOOM_TO_MOUSEPOS = (1 << 20),
   USER_SHOW_FPS = (1 << 21),
   USER_REGISTER_ALL_USERS = (1 << 22),

source/blender/makesrna/intern/rna_userdef.cc

@@ -6263,6 +6263,15 @@ static void rna_def_userdef_input(BlenderRNA *brna)
       "Let the mouse wrap around the view boundaries so mouse movements are not limited by the "
       "screen size (used by transform, dragging of UI controls, etc.)");
 
+  prop = RNA_def_property(srna, "use_accumulative_trackball", PROP_BOOLEAN, PROP_NONE);
+  RNA_def_property_boolean_sdna(prop, NULL, "uiflag", USER_ACCUMULATE_TRACKBALL);
+  RNA_def_property_ui_text(
+      prop,
+      "Continuous Trackball",
+      "Continuously accumulate trackball rotation as the mouse is moved, rather than applying it all at once. "
+      "Allows for more intuitive trackball rotations when moving the mouse a larger distance."
+      );
+
   prop = RNA_def_property(srna, "use_drag_immediately", PROP_BOOLEAN, PROP_NONE);
   RNA_def_property_boolean_sdna(prop, nullptr, "flag", USER_RELEASECONFIRM);
   RNA_def_property_ui_text(prop,