Add warning when drawing with invalid shape constant.

[sansumbrella]

Previously, Java2D renderer silently fails to render LINE_LOOP and LINE_STRIP shapes. This adds a runtime warning when an invalid shape type is specified for the renderer.

Closes #4107

[sansumbrella]

Things that would improve this:

• a compile-time check warning of the line number (hard).
• More details in the run-time error message (unknown difficulty; don't see an int => string conversion for PConstants).

[JakubValtar]

Hi David, thanks for looking into this. To answer your improvement points:

• If you throw IllegalArgumentException(String message) instead of warning, sketch will crash and PDE will highlight the line and display the message. We do both at different places, any preference @benfry?
• You can switch on LINE_STRIP and LINE_LOOP to give customized message for these two and handle unknown constant in the default with a general error message.

Also, we might just want to implement these two instead of printing errors. It's fairly easy on the user side, should be easy on our side too. @benfry?

// LINE_STRIP
noFill();
beginShape();
vertex(...);
endShape();

// LINE_LOOP
noFill();
beginShape();
vertex(...);
endShape(CLOSE);

[benfry]

Both LINE_STRIP and LINE_LOOP should work with the default renderer. Are they not working?

[JakubValtar]

They are not.

[benfry]

Scratch that; they were removed. They're not even in the reference and should probably be taken out of PConstants. They were taken out because LINE_STRIP is handled by using noFill() and endShape(), LINE_LOOP is done with noFill() and endShape(CLOSE).

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