Merge pull request #3 from CesiumGS/feature-metadata

Feature metadata extension (EXT_feature_metadata)

extensions/2.0/Vendor/EXT_feature_metadata/0.0.0/examples/microcosm/README.md

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+## Texture Metadata Example: Microcosm
+
+This glTF example is a mesh that represents a lot of different types of
+terrain in one small tile
+
+This example simulates using per-texel metadata for land cover
+classification as well as the Normalized Difference Vegetation Index (NDVI)
+values.
+
+The data here is hand-made until we can get more realistic data.
+
+### Script to generate metadata
+
+To generate the metadata buffer, run `node microcosm-metadata.js`. This
+will overwrite `microcosm.bin` and print out JSON to add to the bufferViews
+of the glTF.

extensions/2.0/Vendor/EXT_feature_metadata/0.0.0/examples/microcosm/microcosm-metadata.js

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+'use strict';
+
+const fs = require('fs');
+
+/**
+ * Need to know these lengths:
+ * - total buffer length
+ *
+ * - LULC Name bufferView length and offsets
+ * - LULC Name offsets bufferView length and offsets
+ * - LULC Color bufferView length and offsets
+ */
+
+// This is how I mapped the color values in GIMP. Kinda haphazard admittedly.
+const landCoverValues = {
+    0: {
+        name: "Grassland",
+        color: [118, 163, 11]
+    },
+    32: {
+        name: "Rocky Ground",
+        color: [110, 110, 110]
+    },
+    64: {
+        name: "Desert",
+        color: [212, 209, 182]
+    },
+    128: {
+        name: "River",
+        color: [82, 173, 204]
+    },
+    208: {
+        name: "Forest",
+        color: [50, 84, 51]
+    },
+    255: {
+        name: "Building",
+        color: [194, 194, 194]
+    }
+};
+
+const unusedLandCover = {
+    name: "Unused",
+    color: [0, 0, 0]
+};
+
+const numberOfLandCoverFeatures = 256;
+const sizeOfColor = 3;
+
+function makeLandCoverColors() {
+    const bufferLength = numberOfLandCoverFeatures * sizeOfColor;
+    const buffer = Buffer.alloc(bufferLength);
+    for (let i = 0; i < numberOfLandCoverFeatures; i++) {
+        const feature = landCoverValues[i];
+        if (feature !== undefined) {
+            const [r, g, b] = feature.color;
+            buffer[3 * i] = r;
+            buffer[3 * i + 1] = g;
+            buffer[3 * i + 2] = b;
+        }
+
+        // Otherwise the default color of 0, 0, 0 is used,
+        // but the buffer is allocated with all 0s so no work is needed here.
+    }
+    return buffer;
+}
+
+function makeLandCoverNames() {
+    const offsets = new Uint32Array(numberOfLandCoverFeatures + 1);
+    let nameText = '';
+    let currentOffset = 0;
+    for (let i = 0; i < numberOfLandCoverFeatures; i++) {
+        let feature = landCoverValues[i];
+        if (feature === undefined) {
+            feature = unusedLandCover;
+        }
+
+        const name = feature.name;
+        const nameLength = Buffer.byteLength(name, 'utf8');
+
+        offsets[i] = currentOffset;
+        currentOffset += nameLength;
+
+        nameText += name;
+    }
+    offsets[numberOfLandCoverFeatures] = currentOffset;
+
+    const namesBuffer = Buffer.from(nameText, 'utf8');
+
+    // Convert from Uint32Array -> Buffer (which is a Uint8Array)
+    const offsetsBuffer = Buffer.from(offsets.buffer);
+    return [namesBuffer, offsetsBuffer];
+}
+
+function makeBufferViews() {
+    const [landCoverNames, landCoverOffsets] = makeLandCoverNames();
+    const landCoverColor = makeLandCoverColors();
+
+    return [
+        {
+            name: "LULC Name",
+            bufferView: landCoverNames
+        },
+        {
+            name: "LULC Name Offsets",
+            bufferView: landCoverOffsets,
+        },
+        {
+            name: "LULC Color",
+            bufferView: landCoverColor
+        }
+    ]
+}
+
+function makeBinFile() {
+    const bufferViewInfos = makeBufferViews();
+    const bufferViews = [];
+    const stats = [];
+    let offset = 0;
+    for (const bufferViewInfo of bufferViewInfos) {
+        if (offset % 8 != 0) {
+            const paddingBytes = 8 - (offset % 8);
+            console.log(`Offset not aligned, adding ${paddingBytes} of padding`);
+            const padding = Buffer.alloc(paddingBytes);
+            bufferViews.push(padding);
+            offset += paddingBytes;
+        }
+
+        const bufferView = bufferViewInfo.bufferView;
+        const byteLength = bufferView.byteLength;
+        stats.push({
+            name: bufferViewInfo.name,
+            buffer: 1,
+            byteLength: byteLength,
+            byteOffset: offset
+        });
+        offset += byteLength;
+
+        bufferViews.push(bufferView);
+    }
+
+    const buffer = Buffer.concat(bufferViews);
+    fs.writeFileSync('microcosm-metadata.bin', buffer, 'utf8');
+
+    console.log(JSON.stringify(stats, undefined, 4));
+    console.log('totalLength:', buffer.byteLength);
+}
+
+makeBinFile();