T54991: Restore support for Motion Path drawing in 2.8

This commit restores support for Motion Path drawing in 2.8 (as it wasn't ported over
to the new draw engines earlier, and the existing space_view3d/drawanimviz.c code was
removed during the Blender Internal removal).

Notes:
* Motion Paths are now implemented as an overlay (enabled by default).
  Therefore, you can turn all of them on/off from the "Overlays" popover

* By and large, we have kept the same draw style as was used in 2.7
  Further changes can happen later following further design work.

* One change from 2.7 is that thicker lines are used by default (2px vs 1px)


Todo's:
* There are some bad-level calls introduced here (i.e. the actgroup_to_keylist() stuff).
  These were introduced to optimise drawing performance (by avoiding full keyframes -> keylist
  conversion step on each drawcall). Instead, this has been moved to the calculation step
  (in blenkernel).  Soon, there will be some cleanups/improvements with those functions,
  so until then, we'll keep the bad level calls.


Credits:
* Clément Foucault (fclem) - Draw Engine magic + Shader Conversion/Optimisation
* Joshua Leung (Aligorith) - COW fixes, UI integration, etc.


Revision History:
See "tmp-b28-motionpath_drawing" branch (rBa12ab5b2ef49ccacae091ccb54d72de0d63f990d)

1 files changed, 47 insertions, 0 deletions

diff --git a/source/blender/draw/modes/shaders/animviz_mpath_points_vert.glsl b/source/blender/draw/modes/shaders/animviz_mpath_points_vert.glsl
new file mode 100644
index 00000000000..3b2f170ca22
--- /dev/null
+++ b/source/blender/draw/modes/shaders/animviz_mpath_points_vert.glsl
@@ -0,0 +1,47 @@
+
+uniform mat4 ViewProjectionMatrix;
+
+uniform int pointSize = 2;
+uniform int frameCurrent;
+uniform int cacheStart;
+uniform bool showKeyFrames = true;
+uniform bool useCustomColor;
+uniform vec3 customColor;
+
+in vec3 pos;
+in int flag;
+
+#define MOTIONPATH_VERT_SEL (1 << 0)
+#define MOTIONPATH_VERT_KEY (1 << 1)
+
+out vec4 finalColor;
+
+void main()
+{
+	gl_Position = ViewProjectionMatrix * vec4(pos, 1.0);
+	gl_PointSize = float(pointSize + 2);
+
+	int frame = gl_VertexID + cacheStart;
+	finalColor = (useCustomColor) ? vec4(customColor, 1.0) : vec4(1.0);
+
+	/* Bias to reduce z fighting with the path */
+	gl_Position.z -= 1e-4;
+
+	if (showKeyFrames) {
+		if ((flag & MOTIONPATH_VERT_KEY) != 0) {
+			gl_PointSize = float(pointSize + 5);
+			finalColor = colorVertexSelect;
+			/* Bias more to get these on top of regular points */
+			gl_Position.z -= 1e-4;
+		}
+		/* Draw big green dot where the current frame is.
+		 * NOTE: this is only done when keyframes are shown, since this adds similar types of clutter
+		 */
+		if (frame == frameCurrent) {
+			gl_PointSize = float(pointSize + 8);
+			finalColor = colorCurrentFrame;
+			/* Bias more to get these on top of keyframes */
+			gl_Position.z -= 1e-4;
+		}
+	}
+}