A new algorithm for polygon clipping in solar calculations for rectangular surfaces

[xuanluo113]

Pull request overview

There exists an extensive amount of literature on polygon clipping when constrained to rectangular surfaces. The current polygon clipping method implemented in EnergyPlus, using the Sutherland-Hodgman algorithm, is a performance hotspot. The method is generalized for clipping area of all shapes, but in EnergyPlus simulations runs, are often called with only rectangular surfaces.

We propose a negligible amount of code to check if the clipping surface is rectangular. And if so,
we redirect to a new method using the Slater & Barsky algorithm.

Pull Request Author

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• Perform a Code Review on GitHub
• If branch is behind develop, merge develop and build locally to check for side effects of the merge
• If defect, verify by running develop branch and reproducing defect, then running PR and reproducing fix
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[nrel-bot]

@XuanLuoLBL @lgentile it has been 28 days since this pull request was last updated.

[nrel-bot]

@XuanLuoLBL @lgentile it has been 28 days since this pull request was last updated.

[mjwitte]

@XuanLuoLBL This needs a unit test, please. Once that's in, please request a reviewer here in the PR.

[mjwitte]

@XuanLuoLBL Needs doc updates, also.

[xuanluo113]

@XuanLuoLBL This needs a unit test, please. Once that's in, please request a reviewer here in the PR.

@mjwitte This branch is also ready for review, as I added those unit tests and documentation.

[xuanluo113]

@Myoldmopar Edwin, this branch is ready for review. Would you please suggest reviewers? Thanks.

[mjwitte]

@xuanluo113 I've reviewed the idd and documentation changes. Comments below.
@Myoldmopar I've done a cursory review of the new code. Would like your eyes on this also.

[mjwitte]

A more complete citation would be good here. And the new functions should have at least a couple of comment lines stating what they do.

[Myoldmopar]

Yeah, this looks fine, but the citation is important. The CLIPLINE and CLIPRECT function names look suspiciously like they were taken from some FORTRAN source. Can you verify where this exact code came from? Also I'm not sure you're going to gain anything by trying to inline this massive function filled with logic.

[xuanluo113]

@Myoldmopar @mjwitte I added the references and am trying to add line comments. I don't think it's borrowed code. It should be based on the algorithm introduced in the paper mimicking the Fortran naming style of other functions.

[mjwitte]

This is hard to read. Apply formatting? Also, seems it would be more efficient to move (NV2==4) to an if block wrapping this so there's no need to check the other conditions if NV2<>4.

[Myoldmopar]

As an FYI, native C++ operators will short circuit, so if NV2 is not 4, it will not evaluate the rest of this. But that said, yeah, this is a big messy expression. I would create three individual terms:

bool const numVertsIs4 = NV2 == 4;
bool const term1 = blah;
bool const term2 = blah;
rectFlat = numVertsIs4 || term1 || term2;

Of course better naming but that would at least make the logic here tractable.

[mjwitte]

@xuanluo113 Be sure to pull this branch before making additional changes. I merged in develop yesterday and fixed the unit tests for the new eio file stuff.

[Myoldmopar]

I made a few comments that should at least be discussed, and maybe requires some code changes.

[Myoldmopar]

As an FYI, native C++ operators will short circuit, so if NV2 is not 4, it will not evaluate the rest of this. But that said, yeah, this is a big messy expression. I would create three individual terms:

bool const numVertsIs4 = NV2 == 4;
bool const term1 = blah;
bool const term2 = blah;
rectFlat = numVertsIs4 || term1 || term2;

Of course better naming but that would at least make the logic here tractable.

[Myoldmopar]

Yeah, this looks fine, but the citation is important. The CLIPLINE and CLIPRECT function names look suspiciously like they were taken from some FORTRAN source. Can you verify where this exact code came from? Also I'm not sure you're going to gain anything by trying to inline this massive function filled with logic.

[xuanluo113]

@Myoldmopar @mjwitte I've addressed all comments except for the coding style and comment ones for the two newly added solar clipping functions. Still working on this.

[Myoldmopar]

Regressions locally look all clean, just eio diffs. I'm merging this.

[xuanluo113]

Regressions locally look all clean, just eio diffs. I'm merging this.

thanks.