Add tests for viewing depth with ClearBeforeDraw.

Also updated documentation/README files to reflect the changes and
help others get up to speed on editing tests/documentation.

docs/README.md

@@ -0,0 +1,18 @@
+# RenderDoc documentation
+
+This readme only covers the documentation. For general information about renderdoc check out [the main github repository](https://github.com/baldurk/renderdoc).
+
+## Generating documentation
+
+Generating the documentation requires the same python version as was used to build the version of RenderDoc you are testing. On windows this is likely python 3.6 as that's what comes with the repository.
+
+The documentation uses restructured text with [Sphinx](http://www.sphinx-doc.org/en/master/). Sphinx can be acquired via `pip install Sphinx`
+
+To generate the documentation, run make.bat or make.sh found in this folder. Run `make help` to see all options, but `make html` is a likely place to start.
+
+License
+--------------
+
+RenderDoc is released under the MIT license, see [the main github repository](https://github.com/baldurk/renderdoc) for full details.
+
+The documentation uses [Sphinx](http://www.sphinx-doc.org/en/master/), which is BSD licensed.

docs/window/texture_viewer.rst

@@ -181,6 +181,8 @@ Gamma display of Linear Data
 
 A proper explanation of this is available in the :ref:`FAQ <gamma-linear-display>`. In short, linear data is 'over-corrected' to look as expected, but this behaviour can be overridden by toggling off this option.
 
+.. _Alpha background:
+
 Alpha background
 ~~~~~~~~~~~~~~~~
 .. |color_wheel| image:: ../imgs/icons/color_wheel.png
@@ -330,8 +332,12 @@ This is a powerful tool for quickly diagnosing issues and can be very useful for
 
 * ``Clipping`` will simply highlight in red any values that are below the current black point (as defined by the range control - see above), and in green any values above the white point. This can be useful in identifying invalid ranges if the range control is adjusted correctly, or in combination with a custom shader visualiser.
 
-* ``Clear before Pass`` will act as if the current target had been cleared to black right before the current pass. This can sometimes make it easier to see the results of a draw, especially if it is blending and only makes a subtle change. If the current API does not have the concept of a pass, it is defined as all the drawcalls with the same set of render targets.
+* ``Clear before Pass`` will act as if the current target had been cleared right before the current pass. This can sometimes make it easier to see the results of a draw, especially if it is blending and only makes a subtle change. If the current API does not have the concept of a pass, it is defined as all the drawcalls with the same set of render targets.
 
+   * If the current target is a render target, it is cleared to the :ref:`Alpha background` color.
+
+   * If the current target is a depth/stencil target, the behavior depends on the depth function for the current draw. If it is ``EQUAL``, ``NOT EQUAL``, or ``ALWAYS``, the target is not cleared. If it is ``LESS`` or ``LESS EQUAL``, it is cleared to 1. If it is ``GREATER`` or ``GREATER EQUAL``, it is cleared to 0. Stencil is never cleared.
+   
 * ``Clear before Draw`` works similarly to the above overlay, but clearing immediately before the selected draw.
 
 * ``Quad Overdraw (Pass)`` will show a visualisation of the level of 2x2 quad overdraw in the 'pass' up to the selected draw. If the current API does not have the concept of a pass, it is defined as all the drawcalls with the same set of render targets.