still has a bug

@@ -876,0 +868,4 @@
+  const int resolution_x = (int)((bezt->vec[1][0] - prevbezt->vec[1][0]) * resolution_scale[0]);
+  const int resolution_y = (int)(fabs(bezt->vec[1][1] - prevbezt->vec[1][1]) *
+                                 resolution_scale[1]);
+  return resolution_x + resolution_y;

@@ -883,0 +878,4 @@
+static void add_bezt_vertices(BezTriple *bezt,
+                              BezTriple *prevbezt,
+                              int resolution,
+                              blender::Vector<blender::float2> &curve_vertices)

@@ -894,0 +892,4 @@
+  float prev_key[2], prev_handle[2], bez_handle[2], bez_key[2];
+  /* Allocation needs +1 on resolution because BKE_curve_forward_diff_bezier uses it to iterate
+   * inclusively. */
+  float *data = static_cast<float *>(

@@ -919,0 +939,4 @@
+  return {first, last};
+}
+
+static void get_extrapolation_point_left(FCurve *fcu,

@@ -892,2 +886,4 @@
   }
 
+  /* If the resolution goes too high the line will not end exactly at the keyframe. Probably due to
+   * accumulating floating point issues in BKE_curve_forward_diff_bezier.*/

@@ -877,4 +873,4 @@
 
 /**
  * Draw a segment from `prevbezt` to `bezt` at the given `resolution`.
  * #immBeginAtMost is expected to be called with enough space for this function to run.

@@ -986,3 +1056,2 @@
-    vertex_position[1] = prevbezt->vec[1][1];
-    immVertex2fv(pos, vertex_position);
+    curve_vertices.append({fcu->bezt[0].vec[1][0], fcu->bezt[0].vec[1][1]});
   }

@@ -990,0 +1059,4 @@
+  const int2 bounding_indices = get_bounding_bezt_indices(fcu, v2d->cur.xmin, v2d->cur.xmax);
+
+  if (bounding_indices[0] == bounding_indices[1]) {
+    BezTriple *bezt = &fcu->bezt[bounding_indices[0]];

@@ -876,0 +875,4 @@
+  const int resolution_y = (int)((max_y - min_y) * resolution_scale[1]);
+  /* The resolution should be the distance between the two keys, but to save the square root
+   * calculation use an approximation by the two values. */
+  return resolution_x + resolution_y;