Add example showing how to use Slang/WASM (#5996)

This closes #5656.

examples/wgpu-slang-wasm/README.md

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+# Simple WebGPU example using Slang WebAssembly library
+
+## Description
+
+This is a simple example showing how WebGPU applications can use the slang-wasm library to compile slang shaders at runtime to WGSL.
+The resulting application shows a green triangle rendered on a black background.
+
+## Instructions
+
+Follow the WebAssembly build instructions in `docs/building.md` to produce `slang-wasm.js` and `slang-wasm.wasm`, and place these files in this directory.
+
+Start a web server, for example by running the following command in this directory:
+
+    $ python -m http.server
+
+Finally, visit `http://localhost:8000/` to see the application running in your browser.

examples/wgpu-slang-wasm/example.js

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+"use strict";
+
+let Example = {
+    initialize: async function (slang, canvas) {
+        async function render(shaders) {
+            if (!navigator.gpu) {
+                throw new Error("WebGPU not supported on this browser.");
+            }
+            const adapter = await navigator.gpu.requestAdapter();
+            if (!adapter) {
+                throw new Error("No appropriate GPUAdapter found.");
+            }
+            const device = await adapter.requestDevice();
+            const context = canvas.getContext("webgpu");
+            const canvasFormat = navigator.gpu.getPreferredCanvasFormat();
+            context.configure({
+                device: device,
+                format: canvasFormat,
+            });
+
+            const vertexBufferLayout = {
+                arrayStride: 8,
+                attributes: [{
+                    format: "float32x2",
+                    offset: 0,
+                    shaderLocation: 0,
+                }],
+            };
+
+            const pipeline = device.createRenderPipeline({
+                label: "Pipeline",
+                layout: "auto",
+                vertex: {
+                    module: device.createShaderModule({
+                        label: "Vertex shader module",
+                        code: shaders.vertex
+                    }),
+                    entryPoint: "vertexMain",
+                    buffers: [vertexBufferLayout]
+                },
+                fragment: {
+                    module: device.createShaderModule({
+                        label: "Fragment shader module",
+                        code: shaders.fragment
+                    }),
+                    entryPoint: "fragmentMain",
+                    targets: [{
+                        format: canvasFormat
+                    }]
+                }
+            });
+
+            const vertices = new Float32Array([
+                0.0, -0.8,
+                +0.8, +0.8,
+                -0.8, +0.8,
+            ]);
+            const vertexBuffer = device.createBuffer({
+                label: "Triangle vertices",
+                size: vertices.byteLength,
+                usage: GPUBufferUsage.VERTEX | GPUBufferUsage.COPY_DST,
+            });
+            const bufferOffset = 0;
+            device.queue.writeBuffer(vertexBuffer, bufferOffset, vertices);
+
+            const encoder = device.createCommandEncoder();
+            const pass = encoder.beginRenderPass({
+                colorAttachments: [{
+                    view: context.getCurrentTexture().createView(),
+                    loadOp: "clear",
+                    clearValue: { r: 0, g: 0, b: 0, a: 1 },
+                    storeOp: "store",
+                }]
+            });
+            pass.setPipeline(pipeline);
+            const vertexBufferSlot = 0;
+            pass.setVertexBuffer(vertexBufferSlot, vertexBuffer);
+            pass.draw(vertices.length / 2);
+            pass.end();
+            const commandBuffer = encoder.finish();
+            device.queue.submit([commandBuffer]);
+        }
+
+        const slangCode = await fetch("shader.slang").then(r => r.text());
+
+        var wasmCompileTarget = null;
+        var compileTargetMap = slang.module.getCompileTargets();
+        for (var i = 0; i < compileTargetMap.length; i++) {
+            var target = compileTargetMap[i];
+            if(target.name == "WGSL") {
+                wasmCompileTarget = target.value;
+            }
+        }
+        if (wasmCompileTarget === null) {
+            throw new Error("Slang/WASM module doesn't support WGSL compile target.");
+        }
+
+        var slangSession = slang.globalSession.createSession(wasmCompileTarget);
+        if (!slangSession) {
+            throw new Error("Failed to create global Slang session.");
+        }
+
+        var wgslShaders = null;
+        try {
+            var module = slangSession.loadModuleFromSource(
+                slangCode, "shader", '/shader.slang'
+            );
+            var vertexEntryPoint = module.findAndCheckEntryPoint(
+                "vertexMain", slang.constants.STAGE_VERTEX
+            );
+            var fragmentEntryPoint = module.findAndCheckEntryPoint(
+                "fragmentMain", slang.constants.STAGE_FRAGMENT
+            );
+            var linkedProgram = slangSession.createCompositeComponentType([
+                module, vertexEntryPoint, fragmentEntryPoint
+            ]).link();
+            wgslShaders = {
+                vertex: linkedProgram.getEntryPointCode(
+                    0 /* entryPointIndex */, 0 /* targetIndex */
+                ),
+                fragment: linkedProgram.getEntryPointCode(
+                    1 /* entryPointIndex */, 0 /* targetIndex */
+                ),
+            };
+        } finally {
+            if (slangSession) {
+                slangSession.delete();
+            }
+        }
+
+        if (!wgslShaders) {
+            throw new Error("Failed to compile WGSL shaders.");
+        }
+
+        render(wgslShaders);
+    }
+}
+
+var Module = {
+    onRuntimeInitialized: function() {
+        const canvas = document.querySelector("canvas");
+
+        var globalSlangSession = Module.createGlobalSession();
+        if (!globalSlangSession) {
+            throw new Error("Failed to create global Slang session.");
+        }
+
+        const slang = {
+            module: Module,
+            globalSession: globalSlangSession,
+            constants: {
+                STAGE_VERTEX: 1,
+                STAGE_FRAGMENT: 5,
+            },
+        };
+        Example.initialize(slang, canvas);
+    },
+};

examples/wgpu-slang-wasm/index.html

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+<html>
+  <head>
+    <title>WebGPU Triangle using Slang WASM</title>
+    <script src="example.js"></script>
+  </head>
+  <body>
+    <center>
+      <canvas width="512" height="512"></canvas>
+    </center>
+    <script src="slang-wasm.js"></script>
+  </body>
+</html>

examples/wgpu-slang-wasm/shader.slang

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+struct VertexStageInput
+{
+    float4 position : POSITION0;
+};
+
+struct VertexStageOutput
+{
+    float4 positionClipSpace : SV_POSITION;
+};
+
+struct FragmentStageOutput
+{
+    float4 color : SV_TARGET;
+};
+
+VertexStageOutput vertexMain(VertexStageInput input) : SV_Position
+{
+	VertexStageOutput output;
+    output.positionClipSpace = float4(input.position.xy, 1);
+    return output;
+}
+
+FragmentStageOutput fragmentMain() : SV_Target
+{
+    FragmentStageOutput output;
+    output.color = float4(0, 1, 0, 1);
+    return output;
+}