More changes...

1 files changed, 68 insertions, 5 deletions

diff --git a/linuxgraphicsdrivers.lyx b/linuxgraphicsdrivers.lyx
index a9a1700..bbf6129 100644
--- a/linuxgraphicsdrivers.lyx
+++ b/linuxgraphicsdrivers.lyx
@@ -253,8 +253,8 @@ reference "cha:The-DRM-Kernel"
 
 \end_inset
 
- introduces the DRM, a kernel module which is in charge of arbitrating all
- graphics activity going on in a Linux system.
+ introduces the Direct Rendering Manager (or DRM), a kernel module which
+ is in charge of arbitrating all graphics activity going on in a Linux system.
  The next chapter (Chapter 
 \begin_inset CommandInset ref
 LatexCommand ref
@@ -3148,6 +3148,12 @@ Interrupts are a way for hardware peripherals in general, and GPUs in particular
 Graphics Hardware Examples
 \end_layout
 
+\begin_layout Subsection
+
+\lang english
+Classical renderers
+\end_layout
+
 \begin_layout Paragraph*
 
 \lang english
@@ -3204,6 +3210,55 @@ Shader engine nv40/nv50
 http://nouveau.freedesktop.org/wiki/HonzaHavlicek
 \end_layout
 
+\begin_layout Subsection
+Deferred Renderers
+\end_layout
+
+\begin_layout Standard
+Deferred renderers are a different design for GPUs.
+ Instead of rendering each 3D primitive as it is submitted by the rendering
+ API, the driver stores it in memory and then issues a single hardware call
+ to render the whole scene.
+ This has a number of advantages over classic architectures:
+\end_layout
+
+\begin_layout Itemize
+Much better rendering locality can be achieved by splitting the screen into
+ tiles (usually in the 32x32 pixel range).
+ The GPU can then iterate over these tiles, and for each of those can resolve
+ per-pixel depth in an internal (mini) zbuffer.
+ Once the whole tile is rendered it can be written back to video memory,
+ saving precious bandwidth.
+ Similarly, since visibility is determined before fetching texture data,
+ only the useful texture data is read, again saving bandwidth.
+\end_layout
+
+\begin_layout Itemize
+If the depth buffer values are not required, they don't need to be written
+ to memory.
+ The depth buffer resolution can happen per-tile inside the GPU and never
+ be written back to video memory, therefore saving video memory bandwith
+ and space.
+\end_layout
+
+\begin_layout Standard
+Of course tiled renders require the ability to store the whole scene in
+ memory before starting, and will also add latency since you need to wait
+ for an end of frame even before you start drawing.
+ The latency problem can be partially hidden by drawing a given frame on
+ the GPU while the driver already allows the application to submit data
+ for the next frame.
+ However in some situations (readbacks, cross-process synchronization) it's
+ not always possible to avoid it.
+\end_layout
+
+\begin_layout Standard
+All in all, the deferred renderers are particularly useful for embedded
+ platforms where the bandwidth is generally very scarce and the applications
+ are simple enough that the additional latency and the limitations of the
+ approach don't matter.
+\end_layout
+
 \begin_layout Paragraph*
 
 \lang english
@@ -3213,13 +3268,20 @@ SGX
 \begin_layout Standard
 
 \lang english
-Tiling architecture
+The SGX is an example of a deferred rendering GPU.
+ It uses a tiling architecture.
+\end_layout
+
+\begin_layout Standard
+
+\lang english
+The SGX shaders combine blending and depth test
 \end_layout
 
 \begin_layout Standard
 
 \lang english
-Combined shader with blending and depth test
+Another example of a deferred renderer is the Mali family of GPUs.
 \end_layout
 
 \begin_layout Standard
@@ -5044,7 +5106,8 @@ name "cha:The-DRM-Kernel"
 
 \lang english
 The use of a kernel module is a requirement in a complex world.
- The kernel module, or DRM, has multiple purposes:
+ This kernel module is called the Direct Rendering Manager (DRM, not to
+ be confused with Digital Rights Management) and serves multiple purposes:
 \end_layout
 
 \begin_layout Itemize