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2 | **
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3 | ** Copyright (C) 2009 Nokia Corporation and/or its subsidiary(-ies).
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40 | ****************************************************************************/
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41 |
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42 | /*!
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43 | \page openvg.html
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44 | \title OpenVG Rendering in Qt
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45 | \since 4.6
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46 | \ingroup best-practices
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47 |
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48 | \brief Efficient rendering on embedded devices with OpenVG
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49 |
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50 | OpenVG is a standard API from the
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51 | \l{http://www.khronos.org/openvg}{Khronos Group} for accelerated
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52 | 2D vector graphics that is appearing in an increasing number of
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53 | embedded devices. The QtOpenVG plugin provides support for OpenVG
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54 | painting.
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55 |
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56 | OpenVG is optimized for 2D vector operations, and closely matches
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57 | the functionality in QPainter. It can therefore be an excellent
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58 | substitute for the default raster-based QPaintEngine on hardware
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59 | that supports OpenVG.
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60 |
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61 | \tableofcontents
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62 |
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63 | \section1 Building Qt with OpenVG support
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64 |
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65 | OpenVG support can be enabled by passing the \c{-openvg} option
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66 | to configure. It is assumed that the following qmake variables
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67 | are set to appropriate values in the qmake.conf file for your
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68 | platform:
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69 |
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70 | \list
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71 | \o QMAKE_INCDIR_OPENVG
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72 | \o QMAKE_LIBDIR_OPENVG
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73 | \o QMAKE_LIBS_OPENVG
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74 | \endlist
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75 |
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76 | Most OpenVG implementations are based on EGL, so the following
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77 | variables may also need to be set:
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78 |
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79 | \list
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80 | \o QMAKE_INCDIR_EGL
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81 | \o QMAKE_LIBDIR_EGL
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82 | \o QMAKE_LIBS_EGL
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83 | \endlist
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84 |
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85 | See \l{qmake Variable Reference} for more information on these variables.
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86 |
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87 | Two kinds of OpenVG engines are currently supported: EGL based,
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88 | and engines built on top of OpenGL such as
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89 | \l{http://sourceforge.net/projects/shivavg}{ShivaVG}.
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90 | EGL based engines are preferred.
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91 |
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92 | It is assumed that the EGL implementation has some way to turn a
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93 | QWidget::winId() into an EGL rendering surface with
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94 | \c{eglCreateWindowSurface()}. If this is not the case, then
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95 | modifications may be needed to the code under \c{src/gui/egl} and
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96 | \c{src/plugins/graphicssystems/openvg} to accomodate the EGL
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97 | implementation.
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98 |
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99 | The ShivaVG graphics system under \c{src/plugins/graphicssystems/shivavg}
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100 | is an example of how to integrate a non-EGL implementation of
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101 | OpenVG into Qt. It is currently only supported with Qt/X11
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102 | and being an example only, the resulting screen output may not
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103 | be as good as with other OpenVG engines.
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104 |
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105 | \section1 Using the OpenVG graphics system
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106 |
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107 | Once the graphics system plugin has been built and installed,
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108 | applications can be run as follows to use the plugin:
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109 |
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110 | \code
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111 | app -graphicssystem OpenVG
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112 | \endcode
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113 |
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114 | If ShivaVG is being used, then substitute \c ShivaVG instead of
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115 | \c OpenVG in the line above.
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116 |
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117 | If the plugin fails to load, try setting the \c QT_DEBUG_PLUGINS
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118 | environment variable to 1 and try again. Usually the plugin
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119 | cannot be loaded because Qt cannot locate it in the directory
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120 | \c{plugins/graphicssystems} within the Qt installation, or the
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121 | dynamic library path does not include the directory containing
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122 | the system's \c libOpenVG.so library.
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123 |
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124 | \section1 Supported features
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125 |
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126 | \section2 Context modes
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127 |
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128 | The default configuration is "single-context" mode, where a single
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129 | EGLContext object is used for all drawing, regardless of the surface.
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130 | Multiple EGLSurfaces are created, one for each window surface or pixmap.
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131 | eglMakeCurrent() is called with the same EGLContext every time, but a
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132 | different EGLSurface.
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133 |
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134 | Single-context mode is necessary for QPixmapData to be implemented in
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135 | terms of a VGImage. If single-context mode is not enabled, then QPixmapData
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136 | will use the fallback QRasterPixmapData implementation, which is less
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137 | efficient performance-wise.
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138 |
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139 | Single-context mode can be disabled with the QVG_NO_SINGLE_CONTEXT define
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140 | if the OpenVG engine does not support one context with multiple surfaces.
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141 |
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142 | \section2 Transformation matrices
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143 |
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144 | All affine and projective transformation matrices are supported.
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145 |
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146 | QVGPaintEngine will use the engine to accelerate affine transformation
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147 | matrices only. When a projective transformation matrix is used,
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148 | QVGPaintEngine will transform the coordinates before passing them
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149 | to the engine. This will probably incur a performance penalty.
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150 |
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151 | Pixmaps and images are always transformed by the engine, because
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152 | OpenVG specifies that projective transformations must work for images.
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153 |
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154 | It is recommended that client applications should avoid using projective
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155 | transformations for non-image elements in performance critical code.
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156 |
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157 | \section2 Composition modes
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