Bug 17148: rasterImage shows incorrect image orientation

[hturner]

This task is to create some test images to help with fixing Bug 17148. It has two parts - the second should only be attempt once the first is completed at least for the Cairo device.

Part 1: Image to check rotation

The following hand-drawn image is intended to demonstrate the documented behaviour of rasterImage:

• The blue square marks the position of the (xleft, ybottom) coordinate
• The red square marks the position of the (xright, ytop) coordinate.
• Based on the blue and red squares, we can determine the direction of the positive x axis (from xleft to xright) and the positive y axis (from ybottom to ytop). These are marked by the arrows labelled x and y.
• Each quadrant shows a square with no rotation (angle = 0) and a rotation of 20 degrees anti-clockwise from positive x-axis about the bottom-left corner (angle = 20)

We expect this image to display correctly on a Cairo device, but incorrectly on other devices. You can draw on a Cairo device by changing the graphics backend in RStudio (Tools > Global Options > General > Graphics > Backend: Cairo) or setting type = "cairo" when opening a file to draw on, e.g.

png("demo.png", type = "cairo)
plot(1:10)
dev.off()

Todo:

• Write some R code based on the raster4() function in Martin Maechler's comment to create the test plot. Use a Cairo device when developing your code.
  • The quadrants in the test plot are reordered from Martin's code: the first column of plots in the test plot corresponds to the second column in Martin's code.
  • Draw each black square based on a raster created from a 4x4 matrix of colours.
  • Redraw the border of each black square using rect(), grid.rect(). When everything is working correctly, this should draw on top of the previous border (you might play with line thickness/colour so we can see the overplotting). When something is not working, it may help us work out what is going wrong.
• Once you have a working plot on the Cairo device, try drawing the plot on the devices below. Create the device using png(type = *) or windows(). You may need to enlist helpers to draw the plot on different operating systems. We expect some or all of these to look incorrect due to the existing bug(s)!
  • Quartz (only available on macOS) - set via RStudio or png()
  • Xlib (only available on macOS/Linux)
  • windows (only available on Windows)

Share your R code and the 4 images (or as many of the 4 images that you can produce) in a comment on this issue.

[hturner]

Part 2: Image to check orientation

In the first part, the raster (black square) was symmetrical about the diagonal from bottom-left (blue square) to top-right (red square). For the second image, we will use a non-symmetrical matrix that depicts an "F" shape:

This will help us check if rasterImage() preserves the order of cells within thewhen the axes are rotated (i.e. when the location of "bottom-left" and "top-right" are not in the same orientation as the canvas). When everything is working correctly, the plot should look something like this:

Warning: we think this will display correctly in the Cairo device, but it might not! Do not adapt the code to fix any problems you see!

Todo:

• Update the R code from part 1 to draw the second image.
  • Plot a single "F" shape with angle = 0 in all four quadrants, using the same (xleft, ybottom) and (xright, ytop) coordinates as before.
  • Draw each F with a raster created from a 4x4 matrix of colours. These F's may not all look correct on the Cairo device, but at least the top-right F should look correct
  • Redraw each F using line() or grid.line() (you might play with line thickness/colour so we can see the overplotting). These F's should look correct on the Cairo device (and hopefully all devices, so we have a correct reference).
• Once you have a working plot on the Cairo device, try drawing the plot on the devices below. We expect some or all of these to look incorrect due to the existing bug(s)!
  • Quartz (only available on macOS) - set via RStudio or png()
  • Xlib (only available on macOS/Linux)
  • windows (only available on Windows)