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authorDavid Boddie <david.boddie@nokia.com>2010-10-08 16:39:09 (GMT)
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- \section1 Hardware Acceleration
-
- When designing applications for embedded devices there is often a
- compromise between graphics effects and performance. On most
- devices, you cannot have both simply because the hardware needed
- for such operations just is not there. With a growing number of
- devices that use hardware dedicated to graphics operations there is
- less need to compromise.
-
- In addition to enabling dynamic graphics effects, there are two
- other benefits to using graphics acceleration. One is that graphics
- acceleration hardware is more power efficient than using the CPU.
- The reason for this is that the CPU might require a clock speed
- that is up to 20 times higher than the GPU, achieving the same
- results. E.g. a typical hardware accelerated mobile graphics unit
- can rasterize one or two bilinear texture fetches in one cycle,
- while a software implementation takes easily more than 20 cycles.
- Typical \e {System-on-a-chip} (SoC) graphics hardware generally have
- a much lower clock speed and memory bandwidth, and different level
- of acceleration than desktop GPUs. One example is that many GPUs
- leave out transformation and lighting from the graphics pipeline
- and only implements rasterization.
-
- Another reason to use a GPU is to offload the main CPU, either for
- power saving or to perform other operations in parallel. Often
- drawing speed with a GPU is not that much faster than a CPU but
- the clear benefit of using the GPU is to free up the CPU to perform
- other tasks which can be used to create a more responsive use
- experience.
-
- The key to writing good applications for devices is therefore to
- limit the wow factor down to what the target hardware can handle,
- and to take advantage of any graphics dedicated hardware. Qt
- provides several ways to both render advanced effects on the screen
- and speed up your application using hardware accelerated graphics.
-
- \tableofcontents
-
- \section2 Qt for Embedded Graphics pipeline
-
- Qt uses QPainter for all graphics operations. By using the same API
- regardless of platform, the code can be reused on different devices.
- QPainter use different paint engines implemented in the QPaintEngine API to
- do the actual painting.
-
- The QPaintEngine API provides paint engines for each window system and
- painting framework supported by Qt. In regards to Qt for Embedded, this
- also includes implementations for OpenGL ES versions 1.1 and 2.0, as well
- as OpenVG and DirectFB(Embedded Linux only).
-
- By using one of these paint engines, you will be able to improve the
- graphics performance of your Qt application. However, if the graphics
- operations used are not supported, this might as well be a trap, slowing
- down your application significantly. This all depends on what kind of
- graphics operations that are supported by the target devices hardware
- configuration.
-
- \image platformHWAcc.png
-
- The paint engine will direct all graphics operations supported by the
- devices hardware to the GPU, and from there they are sent to the
- framebuffer. Unsupported graphics operations falls back to the
- QRasterPaintEngine and are handled by the CPU before sent to the
- framebuffer. In the end, the operating system sends the paint updates off
- to the screen/display. The fallback operation is quite expensive in regards
- to memory consumption, and should be avoided.
-
- \section2 Hardware configuration requirements
-
- Before implementing any application using hardware acceleration, it is wise
- to get an overview of what kind of hardware accelerated graphics operations
- that are available for the target device.
-
- \note On devices with no hardware acceleration, Qt will use
- QRasterPaintEngine, which handles the acceleration using software. On
- devices supporting OpenGL ES, OpenVG or DirectFB(not supported by Windows
- CE), Qt will use the
- respective paint engines to accelerate painting. However, hardware
- configurations that only support a limited set of hardware acceleration
- features, might slow the application graphics down rather than speeding it
- up when using unsupported operations that must fall back to the raster
- engine.
-
- \section3 Different architectures
-
- Based on the architecture used in a device we can make a recommendation on
- which hardware acceleration techniques to use. There are mainly two
- different architectures on embedded devices. These are devices with a
- Unified Memory Architecture (UMA), and devices with dedicated graphics
- memory. Generally, high-end devices will have dedicated graphics memory.
- Low-end devices will just use system memory, sometimes reserving a memory
- region and sometimes not.
-
- In addition to this, we can categorize the devices into five types based on
- the different graphics operations supported by their hardware.
-
- \list 1
- \o No support for graphics acceleration.
- \o Support for blitter and alpha blending.
- \o Support for path based 2D vector graphics.
- \o Support for fixed function 3D graphics.
- \o Support for programmable 3D graphics.
- \endlist
-
- Based on these characteristics the table below recommends which paint
- engines to use with the different types of hardware configurations.
-
- \section3 Recommended use of hardware acceleration based on hardware
-
- \table
- \header
- \o Type
- \o UMA
- \o Non-UMA
- \row
- \o \bold {None}
- \o Qt Raster Engine
- \o Qt Raster Engine
- \row
- \o \bold {Blitter}
- \o DirectFB
- \o DirectFB
- \row
- \o \bold {2D Vector}
- \o OpenVG
- \o OpenVG
- \row
- \o \bold {Fixed 3D}
- \o OpenGL (ES) 1.x
- \o OpenGL (ES) 1.x
- \row
- \o \bold {Programmable 3D}
- \o OpenGL (ES) 2.x
- \o OpenGL (ES) 2.x
- \endtable
-
- \note Since the DirectFB API is quite primitive, the raster paint engine
- handles most of the operations.
-
- \note Blitter and Alpha blending is currently not supported on Windows CE.
+\section1 Hardware Acceleration
+
+When designing applications for embedded devices there is often a
+compromise between graphics effects and performance. On most
+devices, you cannot have both simply because the hardware needed
+for such operations just is not there. With a growing number of
+devices that use hardware dedicated to graphics operations there is
+less need to compromise.
+
+In addition to enabling dynamic graphics effects, there are two
+other benefits to using graphics acceleration. One is that graphics
+acceleration hardware is more power efficient than using the CPU.
+The reason for this is that the CPU might require a clock speed
+that is up to 20 times higher than the GPU, achieving the same
+results. E.g. a typical hardware accelerated mobile graphics unit
+can rasterize one or two bilinear texture fetches in one cycle,
+while a software implementation takes easily more than 20 cycles.
+Typical \e {System-on-a-chip} (SoC) graphics hardware generally have
+a much lower clock speed and memory bandwidth, and different level
+of acceleration than desktop GPUs. One example is that many GPUs
+leave out transformation and lighting from the graphics pipeline
+and only implements rasterization.
+
+Another reason to use a GPU is to offload the main CPU, either for
+power saving or to perform other operations in parallel. Often
+drawing speed with a GPU is not that much faster than a CPU but
+the clear benefit of using the GPU is to free up the CPU to perform
+other tasks which can be used to create a more responsive use
+experience.
+
+The key to writing good applications for devices is therefore to
+limit the wow factor down to what the target hardware can handle,
+and to take advantage of any graphics dedicated hardware. Qt
+provides several ways to both render advanced effects on the screen
+and speed up your application using hardware accelerated graphics.
+
+\tableofcontents
+
+\section2 Qt for Embedded Graphics pipeline
+
+Qt uses QPainter for all graphics operations. By using the same API
+regardless of platform, the code can be reused on different devices.
+QPainter use different paint engines implemented in the QPaintEngine API to
+do the actual painting.
+
+The QPaintEngine API provides paint engines for each window system and
+painting framework supported by Qt. In regards to Qt for Embedded, this
+also includes implementations for OpenGL ES versions 1.1 and 2.0, as well
+as OpenVG and DirectFB(Embedded Linux only).
+
+By using one of these paint engines, you will be able to improve the
+graphics performance of your Qt application. However, if the graphics
+operations used are not supported, this might as well be a trap, slowing
+down your application significantly. This all depends on what kind of
+graphics operations that are supported by the target devices hardware
+configuration.
+
+\image platformHWAcc.png
+
+The paint engine will direct all graphics operations supported by the
+devices hardware to the GPU, and from there they are sent to the
+framebuffer. Unsupported graphics operations falls back to the
+QRasterPaintEngine and are handled by the CPU before sent to the
+framebuffer. In the end, the operating system sends the paint updates off
+to the screen/display. The fallback operation is quite expensive in regards
+to memory consumption, and should be avoided.
+
+\section2 Hardware configuration requirements
+
+Before implementing any application using hardware acceleration, it is wise
+to get an overview of what kind of hardware accelerated graphics operations
+that are available for the target device.
+
+\note On devices with no hardware acceleration, Qt will use
+QRasterPaintEngine, which handles the acceleration using software. On
+devices supporting OpenGL ES, OpenVG or DirectFB(not supported by Windows
+CE), Qt will use the
+respective paint engines to accelerate painting. However, hardware
+configurations that only support a limited set of hardware acceleration
+features, might slow the application graphics down rather than speeding it
+up when using unsupported operations that must fall back to the raster
+engine.
+
+\section3 Different architectures
+
+Based on the architecture used in a device we can make a recommendation on
+which hardware acceleration techniques to use. There are mainly two
+different architectures on embedded devices. These are devices with a
+Unified Memory Architecture (UMA), and devices with dedicated graphics
+memory. Generally, high-end devices will have dedicated graphics memory.
+Low-end devices will just use system memory, sometimes reserving a memory
+region and sometimes not.
+
+In addition to this, we can categorize the devices into five types based on
+the different graphics operations supported by their hardware.
+
+\list 1
+ \o No support for graphics acceleration.
+ \o Support for blitter and alpha blending.
+ \o Support for path based 2D vector graphics.
+ \o Support for fixed function 3D graphics.
+ \o Support for programmable 3D graphics.
+\endlist
+
+Based on these characteristics the table below recommends which paint
+engines to use with the different types of hardware configurations.
+
+\section3 Recommended use of hardware acceleration based on hardware
+
+\table
+ \header
+ \o Type
+ \o UMA
+ \o Non-UMA
+ \row
+ \o \bold {None}
+ \o Qt Raster Engine
+ \o Qt Raster Engine
+ \row
+ \o \bold {Blitter}
+ \o DirectFB
+ \o DirectFB
+ \row
+ \o \bold {2D Vector}
+ \o OpenVG
+ \o OpenVG
+ \row
+ \o \bold {Fixed 3D}
+ \o OpenGL (ES) 1.x
+ \o OpenGL (ES) 1.x
+ \row
+ \o \bold {Programmable 3D}
+ \o OpenGL (ES) 2.x
+ \o OpenGL (ES) 2.x
+\endtable
+
+\note Since the DirectFB API is quite primitive, the raster paint engine
+handles most of the operations.
+
+\note Blitter and Alpha blending is currently not supported on Windows CE.