Convert Canvas to NAPI

[aruneshchandra]

No description provided.

[aruneshchandra]

Depends on #50 Typed Arrays

[jasongin]

I've already partially ported the canvas package to NAPI as part of #41; see related information there. The remaining work items are:

1. Update already-ported canvas code for recent NAPI changes (error-handling)
2. Add typed-arrays support to NAPI (Typed arrays #50)
3. Port the small parts of canvas code that use typed-arrays to NAPI.
4. Validate the port using canvas's tests, and fix any bugs caused by porting.

[jasongin]

I updated the Canvas port to use the new NAPI C++ wrapper classes. It still needs typed-array support.

[jasongin]

With typed arrays in the NAPI C API (#90) and the wrapper (#88), I was able to complete the canvas port. All the canvas tests are now passing on the NAPI port! I will try benchmarking it next.

[jasongin]

Canvas performance testing is tracked as a separate task (#77), so this one can be closed.

The code is at https://github.com/jasongin/node-canvas/tree/napi2

[jasongin]

While trying to benchmark canvas, I found a bug that is related to some Nan::ObjectWrap::Ref() / UnRef() calls that I'd forgotten I had commented out when porting the code. The lack of references led to the object being deleted only when under memory pressure, causing benchmarks to crash.

Unfortunately as I investigated further into this area of persistent references and weak references, I realized that current NAPI APIs related to those concepts are insufficient. I think I've heard others mention that, though I don't see any existing issue tracking it, so I'll open one.

Meanwhile I'm reopening this issue, since a fully-working and benchmarkable canvas port will depend on fixing the NAPI referencing APIs.

[jasongin]

Created issue: Weak/strong reference improvements

[aruneshchandra]

Looks like this is done, we should reopen this is there are still issues