[gtk/wip/chergert/glproto] document renderjob internals a bit

[Christian Hergert <chergert src gnome org>]

commit 6326ddaeb5dcd5f599cd0a281d0f1c25bf5914f9
Author: Christian Hergert <chergert redhat com>
Date:   Thu Jan 21 16:12:53 2021 -0800

    document renderjob internals a bit

 gsk/next/gskglrenderjob.c | 65 +++++++++++++++++++++++++++++++++++++----------
 1 file changed, 52 insertions(+), 13 deletions(-)
---
diff --git a/gsk/next/gskglrenderjob.c b/gsk/next/gskglrenderjob.c
index 313d8eb756..c1e6fd615c 100644
--- a/gsk/next/gskglrenderjob.c
+++ b/gsk/next/gskglrenderjob.c
@@ -74,20 +74,59 @@
 
 struct _GskGLRenderJob
 {
-  GskNextDriver     *driver;
+  /* The driver to be used. This is shared among all the renderers on a given
+   * GdkDisplay and uses the shared GL context to send commands.
+   */
+  GskNextDriver *driver;
+
+  /* The command queue (which is just a faster pointer to the driver's
+   * command queue.
+   */
   GskGLCommandQueue *command_queue;
-  cairo_region_t    *region;
-  guint              framebuffer;
-  graphene_rect_t    viewport;
-  graphene_matrix_t  projection;
-  GArray            *modelview;
-  GArray            *clip;
-  float              alpha;
-  float              offset_x;
-  float              offset_y;
-  float              scale_x;
-  float              scale_y;
-  guint              debug_fallback : 1;
+
+  /* The region that we are clipping. Normalized to a single rectangle region. */
+  cairo_region_t *region;
+
+  /* The framebuffer to draw to in the @context GL context. So 0 would be the
+   * default framebuffer of @context. This is important to note as many other
+   * operations could be done using objects shared from the command queues
+   * GL context.
+   */
+  guint framebuffer;
+
+  /* The viewport we are using. This state is updated as we process render
+   * nodes in the specific visitor callbacks.
+   */
+  graphene_rect_t viewport;
+
+  /* The current projection, updated as we process nodes */
+  graphene_matrix_t projection;
+
+  /* An array of GskGLRenderModelview updated as nodes are processed. The
+   * current modelview is the last element.
+   */
+  GArray *modelview;
+
+  /* An array of GskGLRenderClip updated as nodes are processed. The
+   * current clip is the last element.
+   */
+  GArray *clip;
+
+  /* Our current alpha state as we process nodes */
+  float alpha;
+
+  /* Offset (delta x,y) as we process nodes. Occasionally this is merged into
+   * a transform that is referenced from child transform nodes.
+   */
+  float offset_x;
+  float offset_y;
+
+  /* The scale we are processing, possibly updated by transforms */
+  float scale_x;
+  float scale_y;
+
+  /* If we should be rendering red zones over fallback nodes */
+  guint debug_fallback : 1;
 };
 
 typedef struct GskGLRenderState