`OrthographicProjection`'s public fields are misleading

[xgbwei]

What problem does this solve or what need does it fill?

While working on #6177, I noticed some problems with OrthographicProjection's public fields:

• left, right, bottom, and top, which are used to set the borders of the projection, are public, even though they'll be set automatically if scaling_mode is anything other than ScalingMode::None.

• window_origin affects the origin of the scaling, which means it doesn't have any effect if scaling_mode is ScalingMode::None.

What solution would you like?

• left, right, bottom, and top should be private with public getters. Maybe they can be set through ScalingMode::None's fields; this might make it a bit difficult to update though.

• window_origin should be renamed to scaling_origin or something similar.

What alternative(s) have you considered?

Replace scale with separate width and height values, which will scale the entire projection whether scaling_mode is enabled or not. Then make window_origin (scaling_origin) more flexible with a fractional value of the width and height instead of just WindowOrigin::BottomLeft and WindowOrigin::Center. This will improve usability overall.

[xgbwei]

Just looking for some input here. I can merge this into #6177 (or create a new PR? whatever the conventions is) if it's deemed an issue.

[alice-i-cecile]

I'm on board with all of these changes. I think a second PR is better; smaller PRs are much easier to review and merge.

Your call on which solution you prefer; both seem reasonable to me. The latter is a bit nicer, but less consistent with other camera types.

[bzm3r]

@xgbwei Thanks so much for looking into this ❤️

Working with OrthographicProjection has been a major pain point, so I appreciate it is getting looked at.

About this solution:

Replace scale with separate width and height values, which will scale the entire projection whether scaling_mode is enabled or not. Then make window_origin (scaling_origin) more flexible with a fractional value of the width and height instead of just WindowOrigin::BottomLeft and WindowOrigin::Center. This will improve usability overall.

If you make it scale the entire projection regardless of scaling_mode, then won't this clash with scaling_mode's purpose: https://docs.rs/bevy/latest/bevy/render/camera/enum.ScalingMode.html?

[xgbwei]

If you make it scale the entire projection regardless of scaling_mode, then won't this clash with scaling_mode's purpose: https://docs.rs/bevy/latest/bevy/render/camera/enum.ScalingMode.html?

The width and height values replace scale and the left, right, bottom and top values when applied with ScalingMode::None, but for every scaling mode. That is, they don't affect the size of the viewport and instead only scales the view frustum (the image will stretch if width and height aren't equal).

[bzm3r]

If you make it scale the entire projection regardless of scaling_mode, then won't this clash with scaling_mode's purpose: https://docs.rs/bevy/latest/bevy/render/camera/enum.ScalingMode.html?

The width and height values replace scale and the left, right, bottom and top values when applied with ScalingMode::None, but for every scaling mode. That is, they don't affect the size of the viewport and instead only scales the view frustum (the image will stretch if width and height aren't equal).

Oh, I see! That's important to document then. The view frustrum really provides an "image" which is then stretched into the window.