Use triangle strip for stroke shader

manimlib/mobject/types/vectorized_mobject.py

@@ -51,8 +51,8 @@ DEFAULT_FILL_COLOR = GREY_C
 DISJOINT_CONST = 404
 
 class VMobject(Mobject):
-    stroke_shader_folder: str = "quadratic_bezier_stroke"
     fill_shader_folder: str = "quadratic_bezier_fill"
+    stroke_shader_folder: str = "quadratic_bezier_stroke"
     fill_dtype: Sequence[Tuple[str, type, Tuple[int]]] = [
         ('point', np.float32, (3,)),
         ('orientation', np.float32, (1,)),
@@ -65,7 +65,8 @@ class VMobject(Mobject):
         ("stroke_width", np.float32, (1,)),
         ("color", np.float32, (4,)),
     ]
-    render_primitive: int = moderngl.TRIANGLES
+    fill_render_primitive: int = moderngl.TRIANGLES
+    stroke_render_primitive: int = moderngl.TRIANGLE_STRIP
 
     pre_function_handle_to_anchor_scale_factor: float = 0.01
     make_smooth_after_applying_functions: bool = False
@@ -1135,13 +1136,13 @@ class VMobject(Mobject):
             vert_data=self.fill_data,
             uniforms=self.uniforms,
             shader_folder=self.fill_shader_folder,
-            render_primitive=self.render_primitive,
+            render_primitive=self.fill_render_primitive,
         )
         self.stroke_shader_wrapper = ShaderWrapper(
             vert_data=self.stroke_data,
             uniforms=self.uniforms,
             shader_folder=self.stroke_shader_folder,
-            render_primitive=self.render_primitive,
+            render_primitive=self.stroke_render_primitive,
         )
         self.back_stroke_shader_wrapper = self.stroke_shader_wrapper.copy()
 
@@ -1157,7 +1158,7 @@ class VMobject(Mobject):
         return self.fill_shader_wrapper
 
     def get_stroke_shader_wrapper(self) -> ShaderWrapper:
-        self.stroke_shader_wrapper.vert_data = self.get_stroke_shader_data()[self.get_outer_vert_indices()]
+        self.stroke_shader_wrapper.vert_data = self.get_stroke_shader_data()
         self.stroke_shader_wrapper.uniforms = self.get_shader_uniforms()
         self.stroke_shader_wrapper.depth_test = self.depth_test
         return self.stroke_shader_wrapper
@@ -1197,16 +1198,24 @@ class VMobject(Mobject):
         return [sw for sw in self_sws if len(sw.vert_data) > 0]
 
     def get_stroke_shader_data(self) -> np.ndarray:
+        # Set data array to be one longer than number of points,
+        # with a dummy vertex added at the end. This is to ensure
+        # it can be safely stacked onto other stroke data arrays.
         points = self.get_points()
-        if len(self.stroke_data) != len(points):
-            self.stroke_data = resize_array(self.stroke_data, len(points))
+        n = len(points)
+        size = n + 1 if n > 0 else 0
+        if len(self.stroke_data) != size:
+            self.stroke_data = resize_array(self.stroke_data, size)
+        if n == 0:
+            return self.stroke_data
 
-        self.read_data_to_shader(self.stroke_data, "point", "points")
-        self.read_data_to_shader(self.stroke_data, "color", "stroke_rgba")
-        self.read_data_to_shader(self.stroke_data, "stroke_width", "stroke_width")
+        self.read_data_to_shader(self.stroke_data[:n], "point", "points")
+        self.read_data_to_shader(self.stroke_data[:n], "color", "stroke_rgba")
+        self.read_data_to_shader(self.stroke_data[:n], "stroke_width", "stroke_width")
         self.get_joint_angles()  # Potentially refreshes
-        self.read_data_to_shader(self.stroke_data, "joint_angle", "joint_angle")
+        self.read_data_to_shader(self.stroke_data[:n], "joint_angle", "joint_angle")
 
+        self.stroke_data[-1] = self.stroke_data[-2]
         return self.stroke_data
 
     def get_fill_shader_data(self) -> np.ndarray:

manimlib/shaders/quadratic_bezier_stroke/geom.glsl

@@ -26,6 +26,7 @@ in vec3 verts[3];
 in float v_joint_angle[3];
 in float v_stroke_width[3];
 in vec4 v_color[3];
+in float v_vert_index[3];
 
 out vec4 color;
 out float uv_stroke_width;
@@ -140,6 +141,7 @@ void get_corners(
 
 
 void main() {
+    if (int(v_vert_index[0]) % 2 == 1) return;
     if (distance(verts[0], verts[1]) == 0 || distance(verts[1], verts[2]) == 0) return;
 
     vec3 unit_normal = camera_rotation * vec3(0.0, 0.0, 1.0); // TODO, track true unit normal globally

manimlib/shaders/quadratic_bezier_stroke/vert.glsl

@@ -14,6 +14,7 @@ out vec3 verts;
 out float v_joint_angle;
 out float v_stroke_width;
 out vec4 v_color;
+out float v_vert_index;
 
 const float STROKE_WIDTH_CONVERSION = 0.01;
 
@@ -25,4 +26,5 @@ void main(){
     v_stroke_width = STROKE_WIDTH_CONVERSION * stroke_width * frame_shape[1] / 8.0;
     v_joint_angle = joint_angle;
     v_color = color;
+    v_vert_index = gl_VertexID;
 }