Allow for a clip plane with Surface

manimlib/camera/camera.py

@@ -250,6 +250,12 @@ class Camera(object):
         else:
             self.ctx.disable(moderngl.DEPTH_TEST)
 
+    def set_ctx_clip_distance(self, enable: bool = True) -> None:
+        if enable:
+            gl.glEnable(gl.GL_CLIP_DISTANCE0)
+        else:
+            gl.glDisable(gl.GL_CLIP_DISTANCE0)
+
     def init_light_source(self) -> None:
         self.light_source = Point(self.light_source_position)
 
@@ -377,6 +383,7 @@ class Camera(object):
         shader_program = render_group["prog"]
         self.set_shader_uniforms(shader_program, shader_wrapper)
         self.set_ctx_depth_test(shader_wrapper.depth_test)
+        self.set_ctx_clip_distance(shader_wrapper.use_clip_plane)
         render_group["vao"].render(int(shader_wrapper.render_primitive))
         if render_group["single_use"]:
             self.release_render_group(render_group)

manimlib/mobject/types/surface.py

@@ -66,6 +66,10 @@ class Surface(Mobject):
         )
         self.compute_triangle_indices()
 
+    def init_uniforms(self):
+        super().init_uniforms()
+        self.uniforms["clip_plane"] = np.zeros(4)
+
     def uv_func(self, u: float, v: float) -> tuple[float, float, float]:
         # To be implemented in subclasses
         return (u, v, 0.0)
@@ -207,6 +211,23 @@ class Surface(Mobject):
             surface.sort_faces_back_to_front(vect)
         self.add_updater(updater)
 
+    def set_clip_plane(
+        self,
+        vect: Vect3 | None = None,
+        threshold: float | None = None
+    ):
+        if vect is not None:
+            self.uniforms["clip_plane"][:3] = vect
+        if threshold is not None:
+            self.uniforms["clip_plane"][3] = threshold
+        self.shader_wrapper.use_clip_plane = True
+        return self
+
+    def deactivate_clip_plane(self):
+        self.uniforms["clip_plane"][:] = 0
+        self.shader_wrapper.use_clip_plane = False
+        return self
+
     # For shaders
     def get_shader_data(self) -> np.ndarray:
         s_points, du_points, dv_points = self.get_surface_points_and_nudged_points()

manimlib/shader_wrapper.py

@@ -35,6 +35,7 @@ class ShaderWrapper(object):
         uniforms: dict[str, float] | None = None,  # A dictionary mapping names of uniform variables
         texture_paths: dict[str, str] | None = None,  # A dictionary mapping names to filepaths for textures.
         depth_test: bool = False,
+        use_clip_plane: bool = False,
         render_primitive: int = moderngl.TRIANGLE_STRIP,
     ):
         self.vert_data = vert_data
@@ -44,6 +45,7 @@ class ShaderWrapper(object):
         self.uniforms = uniforms or dict()
         self.texture_paths = texture_paths or dict()
         self.depth_test = depth_test
+        self.use_clip_plane = use_clip_plane
         self.render_primitive = str(render_primitive)
         self.init_program_code()
         self.refresh_id()

manimlib/shaders/surface/vert.glsl

@@ -7,6 +7,7 @@ uniform vec3 camera_position;
 uniform float reflectiveness;
 uniform float gloss;
 uniform float shadow;
+uniform vec4 clip_plane;
 
 in vec3 point;
 in vec3 du_point;
@@ -28,6 +29,10 @@ void main(){
     v_color = color;
     gl_Position = get_gl_Position(xyz_coords);
 
+    if(clip_plane.xyz != vec3(0.0, 0.0, 0.0)){
+        gl_ClipDistance[0] = dot(vec4(point, 1.0), clip_plane);
+    }
+
     v_color = finalize_color(
         color,
         xyz_coords,