[gui] Support rendering lines from a part of VBO (taichi-dev#5495)

* add extra args to support users to draw part of lines they want

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* Update python/taichi/ui/scene.py

Co-authored-by: YuZhang <YuCrazing@users.noreply.github.com>

* fix notes format for docs using

* [pre-commit.ci] auto fixes from pre-commit.com hooks

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* Update python/taichi/ui/scene.py

Co-authored-by: Vissidarte-Herman <93570324+Vissidarte-Herman@users.noreply.github.com>

* Update python/taichi/ui/scene.py

Co-authored-by: Vissidarte-Herman <93570324+Vissidarte-Herman@users.noreply.github.com>

* Update python/taichi/ui/scene.py

Co-authored-by: Vissidarte-Herman <93570324+Vissidarte-Herman@users.noreply.github.com>

* Update python/taichi/ui/scene.py

Co-authored-by: Vissidarte-Herman <93570324+Vissidarte-Herman@users.noreply.github.com>

* imporve the notes of functions in Scene

* skip some tests

* [pre-commit.ci] auto fixes from pre-commit.com hooks

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* test is no problem, github runner goes wrong

* improve notes format

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: YuZhang <YuCrazing@users.noreply.github.com>
Co-authored-by: Vissidarte-Herman <93570324+Vissidarte-Herman@users.noreply.github.com>

python/taichi/ui/scene.py

@@ -93,8 +93,18 @@ def lines(self,
               width,
               indices=None,
               color=(0.5, 0.5, 0.5),
-              per_vertex_color=None):
+              per_vertex_color=None,
+              vertex_offset: int = 0,
+              vertex_count: int = None,
+              index_offset: int = 0,
+              index_count: int = None):
         """Declare multi-lines inside the scene.
+
+        Note that under current situation, for example, there you have 4 vertices,
+        vertices.shape[0] is 4. So there will be 2 lines, the first line's two points
+        are vertices[0] and vertices[1], and the second line's two points are
+        vertices[2] and vertices[3].
+
         Args:
             vertices: a taichi 3D Vector field, where each element indicate the
                 3D location of points of lines.
@@ -106,7 +116,39 @@ def lines(self,
                 If `per_vertex_color` is provided, this is ignored.
             per_vertex_color (Tuple[float]): a taichi 3D vector field, where each
                 element indicate the RGB color of the line.
+            vertex_offset (int, optional):
+                if 'indices' is provided, this refers to the value added to the vertex
+                index before indexing into the vertex buffer, else this refers to the
+                index of the first vertex to draw.
+            vertex_count (int, optional):
+                only available when `indices` is not provided, which is the number
+                of vertices to draw. There are 2 cases that we will change your
+                `vertex_count`. [1] If the `vertex_count` is an odd number, then we
+                will change it to `vertex_count` - 1. [2] If `vertex_offset` plus
+                `vertex_count` greater than vertices.shape[0], then we will reduce
+                `vertex_count` to no more than vertices.shape[0].
+            index_offset (int, optional):
+                Only available when `indices` is provided, which is the base index
+                within the index buffer.
+            index_count (int, optional):
+                Only available when `indices` is provided, which is the number
+                of vertices to draw.
         """
+        if vertex_count is None:
+            vertex_count = vertices.shape[0]
+        if index_count is None:
+            if indices is None:
+                index_count = vertex_count
+            else:
+                index_count = indices.shape[0]
+        if vertex_count % 2:
+            print(
+                "Warning! Odd drawing count will be cut to neast even number")
+            vertex_count -= 1
+        if vertex_count + vertex_offset > vertices.shape[0]:
+            print("Warning! Drawing count greater than shape will be cut")
+            vertex_count = vertices.shape[0] - vertex_offset
+            vertex_count -= vertex_count % 2
         vbo = get_vbo_field(vertices)
         copy_vertices_to_vbo(vbo, vertices)
         has_per_vertex_color = per_vertex_color is not None
@@ -115,7 +157,8 @@ def lines(self,
         vbo_info = get_field_info(vbo)
         indices_info = get_field_info(indices)
         self.scene.lines(vbo_info, indices_info, has_per_vertex_color, color,
-                         width)
+                         width, index_count, index_offset, vertex_count,
+                         vertex_offset)
 
     def mesh(self,
              vertices,
@@ -129,9 +172,11 @@ def mesh(self,
              index_offset: int = 0,
              index_count: int = None):
         """Declare a mesh inside the scene.
+
         if you indicate the index_offset and index_count, the normals will also
         be sliced by the args, and the shading resultes will not be affected.
         (It is equal to make a part of the mesh visible)
+
         Args:
             vertices: a taichi 3D Vector field, where each element indicate the
                 3D location of a vertex.
@@ -147,18 +192,18 @@ def mesh(self,
                 element indicate the RGB color of a vertex.
             two_sided (bool): whether or not the triangles should be able to be
                 seen from both sides.
-            vertex_offset: int type(ohterwise float type will be floored to int),
-                if 'indices' is provided, this means the value added to the vertex
-                index before indexing into the vertex buffer, else this means the
+            vertex_offset (int, optional):
+                if 'indices' is provided, this refers to the value added to the vertex
+                index before indexing into the vertex buffer, else this refers to the
                 index of the first vertex to draw.
-            vertex_count: int type(ohterwise float type will be floored to int),
-                only avaliable when `indices` is not provided, which is the number
+            vertex_count (int, optional):
+                only available when `indices` is not provided, which is the number
                 of vertices to draw.
-            index_offset: int type(ohterwise float type will be floored to int),
-                only avaliable when `indices` is provided, which is the base index
+            index_offset (int, optional):
+                only available when `indices` is provided, which is the base index
                 within the index buffer.
-            index_count: int type(ohterwise float type will be floored to int),
-                only avaliable when `indices` is provided, which is the the number
+            index_count (int, optional):
+                only available when `indices` is provided, which is the the number
                 of vertices to draw.
         """
         vbo = get_vbo_field(vertices)
@@ -199,9 +244,9 @@ def particles(self,
                 values. If `per_vertex_color` is provided, this is ignored.
             per_vertex_color (Tuple[float]): a taichi 3D vector field, where each
                 element indicate the RGB color of a particle.
-            index_offset: int type(ohterwise float type will be floored to int),
+            index_offset (int, optional):
                 the index of the first vertex to draw.
-            index_count: int type(ohterwise float type will be floored to int),
+            index_count (int, optional):
                 the number of vertices to draw.
         """
         vbo = get_vbo_field(centers)

taichi/python/export_ggui.cpp

@@ -140,11 +140,20 @@ struct PyScene {
              FieldInfo indices,
              bool has_per_vertex_color,
              py::tuple color_,
-             float width) {
+             float width,
+             float draw_index_count,
+             float draw_first_index,
+             float draw_vertex_count,
+             float draw_first_vertex) {
     RenderableInfo renderable_info;
     renderable_info.vbo = vbo;
     renderable_info.indices = indices;
     renderable_info.has_per_vertex_color = has_per_vertex_color;
+    renderable_info.has_user_customized_draw = true;
+    renderable_info.draw_index_count = (int)draw_index_count;
+    renderable_info.draw_first_index = (int)draw_first_index;
+    renderable_info.draw_vertex_count = (int)draw_vertex_count;
+    renderable_info.draw_first_vertex = (int)draw_first_vertex;
 
     SceneLinesInfo info;
     info.renderable_info = renderable_info;

taichi/ui/backends/vulkan/renderables/scene_lines.cpp

@@ -69,9 +69,11 @@ void SceneLines::record_this_frame_commands(CommandList *command_list) {
   command_list->set_line_width(curr_width_);
 
   if (indexed_) {
-    command_list->draw_indexed(config_.indices_count, 0, 0);
+    command_list->draw_indexed(config_.draw_index_count,
+                               config_.draw_first_vertex,
+                               config_.draw_first_index);
   } else {
-    command_list->draw(config_.vertices_count, 0);
+    command_list->draw(config_.draw_vertex_count, config_.draw_first_vertex);
   }
 }