RuntimeError: memory access out of bounds

[feedthejim]

hi, it's me again. I'm getting the following error without any ways of debugging (for some reason, Mozilla does't execute my code.

Uncaught (in promise) RuntimeError: memory access out of bounds
    at assembly/Vector3/Vector3#subtract (wasm-function[24]:5)
    at assembly/Sphere/Sphere#intersect (wasm-function[26]:12)
    at assembly/RayTracer/RayTracer#trace (wasm-function[32]:56)
    at assembly/RayTracer/RayTracer#render (wasm-function[33]:309)
    at assembly/index/init (wasm-function[34]:970)
    at WebAssembly.instantiateStreaming.then.module 

Here are the relevants bits of code.

Vector3.ts

  subtract(v2: Vector3): Vector3 {
    return new Vector3(this.x - v2.x, this.y - v2.y, this.z - v2.z);
  }

Sphere.ts

  intersect(rayOrigin: Vector3, rayDirection: Vector3): Intersection | null {
    let l: Vector3 = this.center.subtract(rayOrigin);
  

RayTracer.ts

     let transmission: Vector3 = new Vector3(1, 1, 1);
        let lightDirection = this.elements[i].center
          .subtract(intersectionPoint)
          .normalize();
        for (let j = 0; j < this.elements.length; j++) {
          if (i !== j) {
            let hitInfo: Intersection | null = this.elements[j].intersect(
              intersectionPoint.add(intersectionNormal.multiply(bias)),
              lightDirection,
            );
           

Any idea how I could debug my own code ? What are the best practices when using the arena allocator etc ? I haven't seen any example of using dynamic allocation on any of the projects using assemblyscript.

[MaxGraey]

Can you share full code of Sphere? It might be this.center is null or something else.

btw you can use operator overloading for Vector3 class

[feedthejim]

Can you share full code of Sphere? It might be this.center is null or something else.

I uploaded the code here, I didn't bother to setup the build.

https://webassembly.studio/?f=uzglstt48n

btw you can use operator overloading for Vector3 class

I'm pretty an issue referenced that it wasn't working. (issue #52 ?)

[MaxGraey]

I finished prepare your example and don't see any exceptions:
Update version: https://webassembly.studio/?f=gp6rm11tr5o

Printed result: 2

[MaxGraey]

Which is AssemblyScript version you are use and how to install?

[feedthejim]

  "name": "assembly-script-ray-tracer",
  "version": "1.0.0",
  "description": "A RayTracer built using AssemblyScript",
  "main": "index.js",
  "scripts": {
    "asbuild:untouched": "asc assembly/index.ts -b build/untouched.wasm -t build/untouched.wat --sourceMap --validate --importMemory  --use Math=JSMath",
    "asbuild:optimized": "asc assembly/index.ts -b build/optimized.wasm -t build/optimized.wat --sourceMap --validate --optimize --noDebug --importMemory --use Math=JSMath",
    "asbuild": "npm run asbuild:untouched && npm run asbuild:optimized",
    "server": "http-server . -o -c-1"
  },
  "author": "",
  "license": "ISC",
  "devDependencies": {
    "assemblyscript": "github:AssemblyScript/assemblyscript"
  },
  "dependencies": {
    "glob": "^7.1.2",
    "http-server": "^0.11.1"
  }
}

[feedthejim]

I pushed everything here: https://github.com/feedthejim/AssemblyScriptRayTracer

[dcodeIO]

I believe the error is here: https://github.com/feedthejim/AssemblyScriptRayTracer/blob/master/assembly/RayTracer.ts#L121

That's storing a 32-bit value somewhere where the heap lives in an unsafe way, in turn corrupting the memory. Instead, either use --memoryBase to reserve some fixed-size space at the start of the memory, or use memory.allocate to dynamically allocate a suitable chunk of memory to store to.

See also: Memory Layout & Management

[feedthejim]

Okay, so using the keyword new is definitely not the way to go along with memory.allocate because it doesn't really care if I allocated memory before, right ?

So what's the best way to use and instantiate objects without using new while still using memory allocation ? Creating a pointer and settings the values manually ? ..

[dcodeIO]

The issue isn't with the new keyword in particular, but that you have been mixing dynamic memory allocation and static loads/stores in an unsafe way (here: overwriting each other). If you for example know that you'll need 8kb to store all your static stuff, use --memoryBase 8192 to reserve it before anything else. Compiler-generated static data and the dynamic heap will be placed after that then, so you can freely use those 8KB for manual things, i.e. for a pixel buffer. You can, of course, also allocate the pixel buffer dynamically within the program, for example var pixelBufferStart = memory.allocate(8192) and make your loads and stored relative to that, i.e. var pixelValue = load<u32>(pixelBufferStart + (y * WIDTH + x) * sizeof<u32>()). Now, when accessing the pixel buffer from JS, obtain its start offset through export function getPixelBufferStart(): usize { return pixelBufferStart; } and use an Uint32Array view to work with it.

[MaxGraey]

Closing. You are free to reopen it if there are more questions