From 4b949c07c0ff383e20f007534da34f25f7c545ba Mon Sep 17 00:00:00 2001
From: Lucas Dower <lucasjdower@gmail.com>
Date: Mon, 21 Mar 2022 19:38:22 +0000
Subject: [PATCH] Added support for merging AttributeData

---
 src/buffer.ts       | 39 ++++++++++++++++++++++++
 test/buffer.test.ts | 74 +++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 113 insertions(+)
 create mode 100644 test/buffer.test.ts

diff --git a/src/buffer.ts b/src/buffer.ts
index 53ccf32..bb9524b 100644
--- a/src/buffer.ts
+++ b/src/buffer.ts
@@ -25,6 +25,45 @@ export interface AttributeData {
     }
 }
 
+export function MergeAttributeData(...data: AttributeData[]): AttributeData {
+    if (data.length === 0) {
+        return {
+            indices: new Uint32Array(),
+            custom: {},
+        };
+    }
+    // Check custom attributes match
+    const requiredAttributes = Object.keys(data[0].custom);
+    for (let i = 1; i < data.length; ++i) {
+        const customAttributes = Object.keys(data[i].custom);
+        const isAllRequiredInCustom = requiredAttributes.every((attr) => {
+            return customAttributes.includes(attr);
+        });
+        const isAllCustomInRequired = customAttributes.every((attr) => {
+            return requiredAttributes.includes(attr);
+        });
+        ASSERT(isAllRequiredInCustom && isAllCustomInRequired, 'Attributes to merge do not match');
+    }
+    // Merge data
+    const indices = Array.from(data[0].indices);
+    const custom = data[0].custom;
+    for (let i = 1; i < data.length; ++i) {
+        const nextIndex = Math.max(...indices) + 1;
+        const d = data[i];
+        const newIndices = d.indices.map((index) => index + nextIndex);
+        indices.push(...Array.from(newIndices));
+        for (const attr of requiredAttributes) {
+            const attrData = d.custom[attr];
+            custom[attr].push(...attrData);
+        }
+    }
+
+    return {
+        indices: new Uint32Array(indices),
+        custom: custom,
+    };
+}
+
 export class RenderBuffer {
     private _WebGLBuffer?: {
         buffer: twgl.BufferInfo,
diff --git a/test/buffer.test.ts b/test/buffer.test.ts
new file mode 100644
index 0000000..f17e499
--- /dev/null
+++ b/test/buffer.test.ts
@@ -0,0 +1,74 @@
+import { AttributeData, MergeAttributeData } from '../src/buffer';
+
+test('MergeAttributeData #1', () => {
+    const a: AttributeData = {
+        indices: new Uint32Array([0, 1, 2]),
+        custom: {
+            position: [1, 2, 3, 4, 5, 6, 7, 8, 9],
+            colour: [1, 0, 0, 0, 1, 0, 0, 0, 1],
+        },
+    };
+    const b = MergeAttributeData(a);
+    expect(JSON.stringify(a)).toEqual(JSON.stringify(b));
+});
+
+test('MergeAttributeData #2', () => {
+    const a: AttributeData = {
+        indices: new Uint32Array([0, 1, 2]),
+        custom: {
+            position: [1, 2, 3, 4, 5, 6, 7, 8, 9],
+            colour: [1, 0, 0, 0, 1, 0, 0, 0, 1],
+        },
+    };
+    const b: AttributeData = {
+        indices: new Uint32Array([0, 1, 2]),
+        custom: {
+            position: [10, 11, 12, 13, 14, 15, 16, 17, 18],
+            colour: [0, 1, 1, 1, 0, 1, 1, 1, 0],
+        },
+    };
+    const cActual = MergeAttributeData(a, b);
+    const cExpect: AttributeData = {
+        indices: new Uint32Array([0, 1, 2, 3, 4, 5]),
+        custom: {
+            position: [
+                1,  2,  3,  4,  5,  6,  7,  8,  9,
+                10, 11, 12, 13, 14, 15, 16, 17, 18,
+            ],
+            colour: [
+                1, 0, 0, 0, 1, 0, 0, 0, 1,
+                0, 1, 1, 1, 0, 1, 1, 1, 0,
+            ],
+        },
+    };
+    expect(JSON.stringify(cActual)).toEqual(JSON.stringify(cExpect));
+});
+
+test('MergeAttributeData #3', () => {
+    const a: AttributeData = {
+        indices: new Uint32Array([0, 1]),
+        custom: {
+            data: [1, 2],
+        },
+    };
+    const b: AttributeData = {
+        indices: new Uint32Array([0, 1]),
+        custom: {
+            data: [3, 4],
+        },
+    };
+    const c: AttributeData = {
+        indices: new Uint32Array([0, 1]),
+        custom: {
+            data: [5, 6],
+        },
+    };
+    const dActual = MergeAttributeData(a, b, c);
+    const dExpect: AttributeData = {
+        indices: new Uint32Array([0, 1, 2, 3, 4, 5]),
+        custom: {
+            data: [1, 2, 3, 4, 5, 6],
+        },
+    };
+    expect(JSON.stringify(dActual)).toEqual(JSON.stringify(dExpect));
+});