Performance optimization for builtin httpgd plot viewer

[TTTPOB]

Related nx10/httpgd#113

Hi, this is my first PR to vscode-r, so please let me know if I’ve missed anything in the contribution process.
In the field of bioinformatics, R is often used for single-cell RNA-seq analysis, which typically involves visualizing datasets containing tens of thousands of points.

With the current httpgd SVG viewer in VS Code, rendering such dense plots can become very laggy and unresponsive.
On the other hand, if we disable httpgd and fall back to the naïve PNG viewer, we lose useful features like zoom in/out and dynamic plot resizing.

Motivation

• Large scatter plots (e.g. tens of thousands of points) cause performance issues in the default SVG renderer of httpgd.
• Users need a way to keep httpgd’s interactive features while avoiding SVG rendering bottlenecks.
• Switching between plots in the httpgd plot history currently triggers a full re-render, even when the plot size and zoom level have not changed.

Feature Proposal

1. Support PNG renderer in httpgd plot viewer

   • Added a setting to allow choosing "png" as the renderer for the httpgd viewer, alongside existing formats.
   • This enables users to handle heavy plots more smoothly while retaining httpgd’s interaction features.

2. Plot history caching (planned, not yet implemented in this PR)

   • Cache rendered plots with a key (plotIndex, width, height) to avoid unnecessary redraws when switching between plots of the same size and zoom level.
   • This will improve navigation speed and reduce computation overhead.

Notes

• This PR is currently a draft.
• Only the PNG renderer support is implemented; the caching mechanism will be addressed in a future commit.
• As this is my first PR to vscode-r, I would appreciate guidance on whether the implementation follows the project’s conventions and where improvements can be made.

Thanks for reviewing!

[TTTPOB]

ERROR in C:\Tools\playground\vscode-R\src\test\suite\index.ts
19:32-46
[tsl] ERROR in C:\Tools\playground\vscode-R\src\test\suite\index.ts(19,33)
      TS2345: Argument of type '{ cwd: string; }' is not assignable to parameter of type '(err: Error | null, matches: string[]) => void'.
  Object literal may only specify known properties, and 'cwd' does not exist in type '(err: Error | null, matches: string[]) => void'.

ERROR in C:\Tools\playground\vscode-R\src\test\suite\index.ts
20:13-17
[tsl] ERROR in C:\Tools\playground\vscode-R\src\test\suite\index.ts(20,14)
      TS2339: Property 'then' does not exist on type 'IGlob'.

ERROR in C:\Tools\playground\vscode-R\src\test\suite\index.ts
20:18-23
[tsl] ERROR in C:\Tools\playground\vscode-R\src\test\suite\index.ts(20,19)
      TS7006: Parameter 'files' implicitly has an 'any' type.

ERROR in C:\Tools\playground\vscode-R\src\test\suite\index.ts
22:30-31
[tsl] ERROR in C:\Tools\playground\vscode-R\src\test\suite\index.ts(22,31)
      TS7006: Parameter 'f' implicitly has an 'any' type.

ERROR in C:\Tools\playground\vscode-R\src\test\suite\index.ts
37:19-22
[tsl] ERROR in C:\Tools\playground\vscode-R\src\test\suite\index.ts(37,20)
      TS7006: Parameter 'err' implicitly has an 'any' type.

5 errors have detailed information that is not shown.
Use 'stats.errorDetails: true' resp. '--stats-error-details' to show it.

webpack 5.101.0 compiled with 5 errors and 1 warning in 6909 ms
 ELIFECYCLE  Command failed with exit code 1.

Also, when I run pnpm build, I got this. I don't know if I have to do anything to avoid these errors. I think this is related to #478

[TTTPOB]

Also, I am not sure about commit b3de22b. I don't know if this condition can be removed.
The reason I removed it is otherwise it will stuck into a loop of resizing and redrawing the plot.

[TTTPOB]

r-2.8.6.vsix.zip

I made some adjustment on the test suite issue, so it builds now(changes not in this pr).
This artifact is for review (has included 5d04036 as well).

[TTTPOB]

I accidentally used my master branch to submit this pr so i have to close it. And I think maintainers seems have no spare effort in checking this PR so I will close it. If in the future any maintainer want to reopen it, can leave a message here.