Setting to scale the Canvas to match the width or height of the reference resolution, or a combination.
If the setting is set to 0, the Canvas is scaled according to the difference between the current screen resolution width and the reference resolution width. If the setting is set to 1, the Canvas is scaled according to the difference between the current screen resolution height and the reference resolution height.
For values in between 0 and 1, the scaling is based on a combination of the relative width and height.
Consider an example where the reference resolution of 640x480, and the current screen resolution is a landscape mode of 480x640.
If the scaleWidthOrHeight setting is set to 0, the Canvas is scaled by 0.75 because the current resolution width of 480 is 0.75 times the reference resolution width of 640. The Canvas resolution gets a resolution of 640x853.33. This resolution has the same width as the reference resolution width, but has the aspect ratio of the current screen resolution. Note that the Canvas resolution of 640x853.33 is the current screen resolution divided by the scale factor of 0.75.
If the scaleWidthOrHeight setting is set to 1, the Canvas is scaled by 1.33 because the current resolution height of 640 is 1.33 times the reference resolution height of 480. The Canvas resolution gets a resolution of 360x480. This resolution has the same height as the reference resolution width, but has the aspect ratio of the current screen resolution. Note that the Canvas resolution of 360x480 is the current screen resolution divided by the scale factor of 1.33.
If the scaleWidthOrHeight setting is set to 0.5, we find the horizontal scaling needed (0.75) and the vertical scaling needed (1.33) and find the average. However, we do the average in logarithmic space. A regular average of 0.75 and 1.33 would produce a result of 1.04. However, since multiplying by 1.33 is the same as diving by 0.75, the two scale factor really corresponds to multiplying by 0.75 versus dividing by 0.75, and the average of those two things should even out and produce a neutral result. The average in logarithmic space of 0.75 and 1.33 is exactly 1.0, which is what we want. The Canvas resolution hence ends up being 480x640 which is the current resolution divided by the scale factor of 1.0.
The logic works the same for all values. The average between the horizontal and vertical scale factor is a weighted average based on the matchWidthOrHeight value.