Add wave ballot example

experiments/balloted-splatting/README.md

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+# 2D Differentiable Gaussian Splatting
+
+## About
+
+This example demonstrates the use of Slang and SlangPy to implement a 2D Gaussian splatting algorithm. 
+
+This algorithm represents a simplified version of the 3D Gaussian Splatting algorithm detailed in this paper (https://repo-sam.inria.fr/fungraph/3d-gaussian-splatting/). This 2D demonstration does not have the 3D->2D projection step & assumes that the Gaussian blobs are presented in order of depth (higher index = farther away). Further, this implementation does not perform adaptive density control to add or remove blobs. 
+
+See the `computeDerivativesMain()` kernel and the `splatBlobs()` function for the bulk of the key pieces of the code. This sample uses SlangPy (see `main.py`) to easily load and dispatch the kernels. SlangPy handles the pipeline setup, buffer allocation, buffer copies, and other boilerplate tasks to make it easy to prototype high-performance differentiable code.
+
+For a full 3D Gaussian Splatting implementation written in Slang, see this repository: https://github.com/google/slang-gaussian-rasterization
+
+### Workaround for 'compressing' a 2D group size into a 1D group
+This sample uses a workaround for SlangPy's fixed group size of `(32, 1, 1)`. The rasterizer uses a fixed `8x4` 2D tile. We use numpy commands to construct an aray of dispatch indices such that the right threads receive the right 2D thread index. `calcCompressedDispatchIDs()` in `main.py` holds the logic for this workaround. 
+
+When SlangPy is updated with the functionality to specify group sizes, this workaround will be removed.
+
+## How to Use
+
+### Installation
+
+First, install slangpy and the tev viewer: 
+
+- **SlangPy** python package: `pip install slangpy`. See SlangPy's [docs](https://slangpy.shader-slang.org/en/latest/installation.html) for a full list of requirements.
+- **Tev** viewer: Download from [releases](https://github.com/Tom94/tev/releases/tag/v1.29). See [tev's github](https://github.com/Tom94/tev) for more information.  
+
+Then install the example's requirements, from within the sample folder:
+
+`pip install -r requirements.txt`
+
+### Optional: Setup via Conda
+For simpler setup, use an anaconda/miniconda installation (See [Conda's user guide](https://docs.conda.io/projects/conda/en/latest/user-guide/index.html) for more).
+
+Ensure that your environment is using **Python 3.10**. 
+If you are using conda, you can create a new environment with **python 3.10** and **slangpy** both installed using the following command: 
+`conda create -n slangpy-env python=3.10 slangpy`. Then switch to this new environment with `conda activate slangpy-env`.
+
+### Running the Sample
+- Open the **Tev** viewer and keep it running in the background.
+- From the sample folder, run `python main.py` from a terminal.
+
+You should see a stream of images in Tev as the training progresses:
+
+![](./example-image.png)

experiments/balloted-splatting/app.py

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+# SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+from typing import Callable, Optional
+import slangpy as spy
+from pathlib import Path
+
+
+class App:
+    def __init__(self, title="Balloted Splat Example", width=1024, height=1024, device_type=spy.DeviceType.d3d12):
+        super().__init__()
+
+        # Create a window
+        self._window = spy.Window(
+            width=width, height=height, title=title, resizable=True
+        )
+
+        # Create a device with local include path for shaders
+        self._device = spy.create_device(device_type,
+                                             include_paths=[Path(__file__).parent])
+
+        # Setup swapchain
+        self.surface = self._device.create_surface(self._window)
+        self.surface.configure(width=self._window.width, height=self._window.height)
+
+        self._output_texture: spy.Texture = self.device.create_texture(
+            width=self._window.width,
+            height=self._window.height,
+            format=spy.Format.rgba32_float,
+            usage=spy.TextureUsage.shader_resource | spy.TextureUsage.unordered_access,
+            label="output_texture",
+        )
+
+        # Store mouse pos
+        self._mouse_pos = spy.float2()
+
+        # Internal events
+        self._window.on_keyboard_event = self._on_window_keyboard_event
+        self._window.on_mouse_event = self._on_window_mouse_event
+        self._window.on_resize = self._on_window_resize
+
+        # Hookable events
+        self.on_keyboard_event: Optional[Callable[[spy.KeyboardEvent], None]] = None
+        self.on_mouse_event: Optional[Callable[[spy.MouseEvent], None]] = None
+
+    @property
+    def device(self) -> spy.Device:
+        return self._device
+
+    @property
+    def window(self) -> spy.Window:
+        return self._window
+
+    @property
+    def mouse_pos(self) -> spy.float2:
+        return self._mouse_pos
+
+    @property
+    def output(self) -> spy.Texture:
+        return self._output_texture
+
+    def process_events(self):
+        if self._window.should_close():
+            return False
+        self._window.process_events()
+        return True
+
+    def present(self):
+        image = self.surface.acquire_next_image()
+        if image is None:
+            return
+
+        if (self._output_texture == None
+                or self._output_texture.width != image.width
+                or self._output_texture.height != image.height
+            ):
+            self._output_texture = self.device.create_texture(
+                width=image.width,
+                height=image.height,
+                format=spy.Format.rgba32_float,
+                usage=spy.TextureUsage.shader_resource | spy.TextureUsage.unordered_access,
+                label="output_texture",
+            )
+
+        command_buffer = self._device.create_command_encoder()
+        command_buffer.blit(image, self._output_texture)
+        command_buffer.set_texture_state(image, spy.ResourceState.present)
+        self._device.submit_command_buffer(command_buffer.finish())
+
+        del image
+        self.surface.present()
+
+    def _on_window_keyboard_event(self, event: spy.KeyboardEvent):
+        if event.type == spy.KeyboardEventType.key_press:
+            if event.key == spy.KeyCode.escape:
+                self._window.close()
+                return
+            elif event.key == spy.KeyCode.f1:
+                if self._output_texture:
+                    spy.tev.show_async(self._output_texture)
+                return
+            elif event.key == spy.KeyCode.f2:
+                if self._output_texture:
+                    bitmap = self._output_texture.to_bitmap()
+                    bitmap.convert(
+                        spy.Bitmap.PixelFormat.rgb,
+                        spy.Bitmap.ComponentType.uint8,
+                        srgb_gamma=True,
+                    ).write_async("screenshot.png")
+                return
+        if self.on_keyboard_event:
+            self.on_keyboard_event(event)
+
+    def _on_window_mouse_event(self, event: spy.MouseEvent):
+        if event.type == spy.MouseEventType.move:
+            self._mouse_pos = event.pos
+        if self.on_mouse_event:
+            self.on_mouse_event(event)
+
+    def _on_window_resize(self, width: int, height: int):
+        self._device.wait()
+        self.surface.configure(width=width, height=height)