add basic code documentation

docs/code-docs.md

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+# Code documentation
+
+Some of spmenu's code documented. If you want to hack on the project, this
+should be useful. Note that these may be renamed in the future to make the
+codebase easier to understand and make changes to. Also note that this is
+**definitely not** a complete list.
+
+## Position and width/height variables
+
+- `bh`
+  - Menu height divided by lines gets you `bh`. The name comes from dwm's `bh`
+  meaning 'bar height'. This is the height of each item in the list.
+- `mh`
+  - Menu height (or height of the window)
+  - Use `drw_resize()` and `XResizeWindow()` to adjust this.
+- `mw`
+  - Menu width (or width of the window)
+  - Use `drw_resize()` and `XResizeWindow()` to adjust this.
+  - `2 * borderwidth` is removed from `mw` (2* because we have two sides)
+  - `2 * sp` is removed from `mw` (2* because we have two sides)
+- `x`
+  - X position, functions like `drw_text` use this.
+  - If you set this in bar drawing functions, you must apply the same
+  to `buttonpress()`, otherwise clicks will be offset.
+- `y`
+  - Y position, functions like `drw_text` use this.
+  - If you set this in bar drawing functions, you must apply the same
+  to `buttonpress()`, otherwise clicks will be offset.
+- `ev->x`
+  - X position where you clicked. This is used in the `buttonpress()` function
+  to check where you clicked.
+- `ev->y`
+  - Y position where you clicked. This is used in the `buttonpress()` function
+  to check where you clicked.
+- `w`
+  - Width of something, this is passed to `drw_text()` for example, but you may
+  override this.
+- `plw`
+  - This is the width of the powerline arrow. It must be added on in
+  the `buttonpress()` and draw functions.
+- `vp`
+  - Vertical padding, this is initially added on in the `create_window()` function.
+- `sp`
+  - Horizontal padding, this is initially added on in the `create_window()` function.
+- `promptw`
+  - Width of the prompt text, this is going to be the same as `TEXTW(prompt)`.
+- `inputw`
+  - Width of the input text.
+- `menuposition`
+  - Integer the user is meant to configure. If it's set to `0`, spmenu will be
+  put on the bottom of the screen. If it's set to `1` it will be put on the
+  top of the screen. If it's `2` it will be put in the center of the screen.
+- `wa.width`
+  - Window width, `wa` is `XWindowAttributes`.
+- `wa.height`
+  - Window height, `wa` is `XWindowAttributes`.
+- `imageheight`
+  - Image height, This is **not** the height of the image, it is the height
+  that the image will be scaled to fit.
+- `imagewidth`
+  - Image width, This is **not** the width of the image, it is the width
+  that the image will be scaled to fit.
+- `imagegaps`
+  - Image gaps, this is extra space added around the image.
+- `imageh`
+  - Usually the same as `imageheight`. This is what `imageheight` is initially
+  set to.
+- `imagew`
+  - Usually the same as `imagewidth`. This is what `imagewidth` is initially
+  set to.
+- `imageg`
+  - Usually the same as `imagegaps`. This is what `imagegaps` is initially set to.
+- `longestedge`
+  - As the name implies, it is the longest (highest value) of `imageheight` and `imagewidth`.
+- `numberWidth`
+  - Integer set in some functions, it is simply `TEXTW(numbers)` if the match
+  count isn't hidden.
+- `modeWidth`
+  - Integer set in some functions, it is simply `TEXTW(modetext)` if the mode
+  indicator isn't hidden.
+- `larrowWidth`
+  - Integer set in some functions, it is simply `TEXTW(leftarrow)` if the left
+  arrow isn't hidden.
+- `rarrowWidth`
+  - Integer set in some functions, it is simply `TEXTW(rightarrow)` if the right
+  arrow isn't hidden.
+- `powerlinewidth`
+  - Integer set in some functions, it is simply `plw / 2` if powerlines are enabled.
+- `curpos`
+  - Cursor/caret position. When text is added to the input, the width of that text
+  is added to this.