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<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>WebGPU Text Rendering</title>
</head>

<body>
    <canvas></canvas>
    <script type="module">
        // WebGPU Simple Textured Quad - Import Canvas
        // from https://webgpufundamentals.org/webgpu/webgpu-simple-textured-quad-import-canvas.html


        import { mat4 } from 'https://webgpufundamentals.org/3rdparty/wgpu-matrix.module.js';

        const glyphWidth = 32;
        const glyphHeight = 40;
        const glyphsAcrossTexture = 16;
        function generateGlyphTextureAtlas() {
            const canvas = document.createElement('canvas');
            canvas.width = 512;
            canvas.height = 256;
            const ctx = canvas.getContext('2d');
            ctx.font = '32px monospace';
            ctx.textBaseline = 'middle';
            ctx.textAlign = 'center';
            ctx.fillStyle = 'white';

            for (let c = 33, x = 0, y = 0; c < 128; ++c) {
                ctx.fillText(String.fromCodePoint(c), x + glyphWidth / 2, y + glyphHeight / 2);
                x = (x + glyphWidth) % canvas.width;
                if (x === 0) y += glyphHeight;
            }

            return canvas;
        }

        async function main() {
            const adapter = await navigator.gpu?.requestAdapter();
            const device = await adapter?.requestDevice();
            if (!device) {
                fail('need a browser that supports WebGPU');
                return;
            }

            // Get a WebGPU context from the canvas and configure it
            const canvas = document.querySelector('canvas');
            const context = canvas.getContext('webgpu');
            const presentationFormat = navigator.gpu.getPreferredCanvasFormat();
            context.configure({
                device,
                format: presentationFormat,
            });

            const module = device.createShaderModule({
                label: 'our hardcoded textured quad shaders',
                code: `
      struct VSInput {
        @location(0) position: vec4f,
        @location(1) texcoord: vec2f,
        @location(2) color: vec4f,
      };

      struct VSOutput {
        @builtin(position) position: vec4f,
        @location(0) texcoord: vec2f,
        @location(1) color: vec4f,
      };

      struct Uniforms {
        matrix: mat4x4f,
      };

      @group(0) @binding(2) var<uniform> uni: Uniforms;

      @vertex fn vs(vin: VSInput) -> VSOutput {
        var vsOutput: VSOutput;
        vsOutput.position = uni.matrix * vin.position;
        vsOutput.texcoord = vin.texcoord;
        vsOutput.color = vin.color;
        return vsOutput;
      }

      @group(0) @binding(0) var ourSampler: sampler;
      @group(0) @binding(1) var ourTexture: texture_2d<f32>;

      @fragment fn fs(fsInput: VSOutput) -> @location(0) vec4f {
        return textureSample(ourTexture, ourSampler, fsInput.texcoord) * fsInput.color;
      }
    `,
            });

            const glyphCanvas = genreateGlyphTextureAtlas();
            // so we can see it
            document.body.appendChild(glyphCanvas);
            glyphCanvas.style.backgroundColor = '#222';

            const maxGlyphs = 100;
            const floatsPerVertex = 2 + 2 + 4; // 2(pos) + 2(texcoord) + 4(color)
            const vertexSize = floatsPerVertex * 4; // 4 bytes each float
            const vertsPerGlyph = 6;
            const vertexBufferSize = maxGlyphs * vertsPerGlyph * vertexSize;
            const vertexBuffer = device.createBuffer({
                label: 'vertices',
                size: vertexBufferSize,
                usage: GPUBufferUsage.VERTEX | GPUBufferUsage.COPY_DST,
            });
            const indexBuffer = device.createBuffer({
                label: 'indices',
                size: maxGlyphs * vertsPerGlyph * 4,
                usage: GPUBufferUsage.INDEX | GPUBufferUsage.COPY_DST,
            });
            // pre fill index buffer with quad indices
            {
                const indices = [];
                for (let i = 0; i < maxGlyphs; ++i) {
                    const ndx = i * 4;
                    indices.push(ndx, ndx + 1, ndx + 2, ndx + 2, ndx + 1, ndx + 3);
                }
                device.queue.writeBuffer(indexBuffer, 0, new Uint32Array(indices));
            }

            function generateGlyphVerticesForText(s, colors = [[1, 1, 1, 1]]) {
                const vertexData = new Float32Array(maxGlyphs * floatsPerVertex * vertsPerGlyph);
                const glyphUVWidth = glyphWidth / glyphCanvas.width;
                const glyphUVheight = glyphHeight / glyphCanvas.height;
                let offset = 0;
                let x0 = 0;
                let x1 = 1;
                let y0 = 0;
                let y1 = 1;
                let width = 0;

                const addVertex = (x, y, u, v, r, g, b, a) => {
                    vertexData[offset++] = x;
                    vertexData[offset++] = y;
                    vertexData[offset++] = u;
                    vertexData[offset++] = v;
                    vertexData[offset++] = r;
                    vertexData[offset++] = g;
                    vertexData[offset++] = b;
                    vertexData[offset++] = a;
                };

                const spacing = 0.55;
                let colorNdx = 0;
                for (let i = 0; i < s.length; ++i) {
                    // convert char code to texcoords for glyph texture
                    const c = s.charCodeAt(i);
                    if (c >= 33) {
                        const cNdx = c - 33;
                        const glyphX = cNdx % glyphsAcrossTexture;
                        const glyphY = Math.floor(cNdx / glyphsAcrossTexture);
                        const u0 = (glyphX * glyphWidth) / glyphCanvas.width;
                        const v1 = (glyphY * glyphHeight) / glyphCanvas.height;
                        const u1 = u0 + glyphUVWidth;
                        const v0 = v1 + glyphUVheight;
                        width = Math.max(x1, width);

                        addVertex(x0, y0, u0, v0, ...colors[colorNdx]);
                        addVertex(x1, y0, u1, v0, ...colors[colorNdx]);
                        addVertex(x0, y1, u0, v1, ...colors[colorNdx]);
                        addVertex(x1, y1, u1, v1, ...colors[colorNdx]);
                    } else {
                        colorNdx = (colorNdx + 1) % colors.length;
                        if (c === 10) {
                            x0 = 0;
                            x1 = 1;
                            y0 = y0 - 1;
                            y1 = y0 + 1;
                            continue;
                        }
                    }
                    x0 = x0 + spacing;
                    x1 = x0 + 1;
                }

                return {
                    vertexData,
                    numGlyphs: offset / floatsPerVertex,
                    width,
                    height: y1,
                };
            }

            const { vertexData, numGlyphs, width, height } = generateGlyphVerticesForText(
                'Hello\nworld!\nText in\nWebGPU!', [
                [1, 1, 0, 1],
                [0, 1, 1, 1],
                [1, 0, 1, 1],
                [1, 0, 0, 1],
                [0, .5, 1, 1],
            ]);
            device.queue.writeBuffer(vertexBuffer, 0, vertexData);

            const pipeline = device.createRenderPipeline({
                label: 'hardcoded textured quad pipeline',
                layout: 'auto',
                vertex: {
                    module,
                    entryPoint: 'vs',
                    buffers: [
                        {
                            arrayStride: vertexSize,
                            attributes: [
                                { shaderLocation: 0, offset: 0, format: 'float32x2' },  // position
                                { shaderLocation: 1, offset: 8, format: 'float32x2' },  // texcoord
                                { shaderLocation: 2, offset: 16, format: 'float32x4' },  // color
                            ],
                        },
                    ],
                },
                fragment: {
                    module,
                    entryPoint: 'fs',
                    targets: [
                        {
                            format: presentationFormat,
                            blend: {
                                color: {
                                    srcFactor: 'one',
                                    dstFactor: 'one-minus-src-alpha',
                                    operation: 'add',
                                },
                                alpha: {
                                    srcFactor: 'one',
                                    dstFactor: 'one-minus-src-alpha',
                                    operation: 'add',
                                },
                            },
                        },
                    ],
                },
            });

            function copySourceToTexture(device, texture, source, { flipY } = {}) {
                device.queue.copyExternalImageToTexture(
                    { source, flipY, },
                    { texture, premultipliedAlpha: true },
                    { width: source.width, height: source.height },
                );
            }

            function createTextureFromSource(device, source, options = {}) {
                const texture = device.createTexture({
                    format: 'rgba8unorm',
                    size: [source.width, source.height],
                    usage: GPUTextureUsage.TEXTURE_BINDING |
                        GPUTextureUsage.COPY_DST |
                        GPUTextureUsage.RENDER_ATTACHMENT,
                });
                copySourceToTexture(device, texture, source, options);
                return texture;
            }

            const texture = createTextureFromSource(device, glyphCanvas, { mips: true });
            const sampler = device.createSampler({
                minFilter: 'linear',
                magFilter: 'linear',
            });

            // create a buffer for the uniform values
            const uniformBufferSize =
                16 * 4; // matrix is 16 32bit floats (4bytes each)
            const uniformBuffer = device.createBuffer({
                label: 'uniforms for quad',
                size: uniformBufferSize,
                usage: GPUBufferUsage.UNIFORM | GPUBufferUsage.COPY_DST,
            });

            // create a typedarray to hold the values for the uniforms in JavaScript
            const kMatrixOffset = 0;
            const uniformValues = new Float32Array(uniformBufferSize / 4);
            const matrix = uniformValues.subarray(kMatrixOffset, 16);

            const bindGroup = device.createBindGroup({
                layout: pipeline.getBindGroupLayout(0),
                entries: [
                    { binding: 0, resource: sampler },
                    { binding: 1, resource: texture.createView() },
                    { binding: 2, resource: { buffer: uniformBuffer } },
                ],
            });

            const renderPassDescriptor = {
                label: 'our basic canvas renderPass',
                colorAttachments: [
                    {
                        // view: <- to be filled out when we render
                        clearValue: [0.3, 0.3, 0.3, 1],
                        loadOp: 'clear',
                        storeOp: 'store',
                    },
                ],
            };

            function render(time) {
                time *= 0.001;

                const fov = 60 * Math.PI / 180;  // 60 degrees in radians
                const aspect = canvas.clientWidth / canvas.clientHeight;
                const zNear = 0.001;
                const zFar = 50;
                const projectionMatrix = mat4.perspective(fov, aspect, zNear, zFar);

                const cameraPosition = [0, 0, 5];
                const up = [0, 1, 0];
                const target = [0, 0, 0];
                const viewMatrix = mat4.lookAt(cameraPosition, target, up);
                const viewProjectionMatrix = mat4.multiply(projectionMatrix, viewMatrix);

                // Get the current texture from the canvas context and
                // set it as the texture to render to.
                renderPassDescriptor.colorAttachments[0].view =
                    context.getCurrentTexture().createView();

                const encoder = device.createCommandEncoder({
                    label: 'render quad encoder',
                });
                const pass = encoder.beginRenderPass(renderPassDescriptor);
                pass.setPipeline(pipeline);

                mat4.rotateY(viewProjectionMatrix, time, matrix);
                mat4.translate(matrix, [-width / 2, -height / 2, 0], matrix);

                // copy the values from JavaScript to the GPU
                device.queue.writeBuffer(uniformBuffer, 0, uniformValues);

                pass.setBindGroup(0, bindGroup);
                pass.setVertexBuffer(0, vertexBuffer);
                pass.setIndexBuffer(indexBuffer, 'uint32');
                pass.drawIndexed(numGlyphs * 6);

                pass.end();

                const commandBuffer = encoder.finish();
                device.queue.submit([commandBuffer]);

                requestAnimationFrame(render);
            }
            requestAnimationFrame(render);
        }

        function fail(msg) {
            // eslint-disable-next-line no-alert
            alert(msg);
        }

        main();

    </script>
</body>

</html>