📄 视区和裁剪viewports and clipping.htm
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lang=EN-US>0.0到1.0），在这之间的场景会被渲染。<o:p></o:p></SPAN></SPAN></P>
<P class=MsoNormal
style="mso-margin-top-alt: auto; mso-margin-bottom-alt: auto"><SPAN
style="FONT-FAMILY: 宋体; mso-bidi-font-family: 宋体; mso-fareast-language: ZH-CN">本节讨论裁剪，即几何流水线的最后一步。讨论被分为以下主题。<SPAN
lang=EN-US><o:p></o:p></SPAN></SPAN></P>
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lang=EN-US
style="FONT-SIZE: 10pt; FONT-FAMILY: Symbol; mso-bidi-font-family: Symbol; mso-fareast-language: ZH-CN; mso-fareast-font-family: Symbol; mso-bidi-font-size: 12.0pt"><SPAN
style="mso-list: Ignore">·<SPAN
style="FONT: 7pt 'Times New Roman'">
</SPAN></SPAN></SPAN><![endif]><U><SPAN lang=EN-US
style="FONT-FAMILY: 宋体; mso-bidi-font-family: 宋体; mso-fareast-language: ZH-CN"><A
href="http://www.gesoftfactory.com/developer/VnC.htm#视区矩形">视区矩形</A></SPAN></U><SPAN
lang=EN-US
style="FONT-FAMILY: 宋体; mso-bidi-font-family: 宋体; mso-fareast-language: ZH-CN"><o:p></o:p></SPAN></P>
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style="MARGIN-LEFT: 36pt; TEXT-INDENT: -18pt; mso-margin-top-alt: auto; mso-margin-bottom-alt: auto; tab-stops: list 36.0pt; mso-list: l0 level1 lfo2; mso-list-change: SGuy 20030510T1452"><![if !supportLists]><SPAN
lang=EN-US
style="FONT-SIZE: 10pt; FONT-FAMILY: Symbol; mso-bidi-font-family: Symbol; mso-fareast-language: ZH-CN; mso-fareast-font-family: Symbol; mso-bidi-font-size: 12.0pt"><SPAN
style="mso-list: Ignore">·<SPAN
style="FONT: 7pt 'Times New Roman'">
</SPAN></SPAN></SPAN><![endif]><U><SPAN lang=EN-US
style="FONT-FAMILY: 宋体; mso-bidi-font-family: 宋体; mso-fareast-language: ZH-CN"><A
href="http://www.gesoftfactory.com/developer/VnC.htm#视棱锥">视棱锥</A></SPAN></U><SPAN
lang=EN-US
style="FONT-FAMILY: 宋体; mso-bidi-font-family: 宋体; mso-fareast-language: ZH-CN"><o:p></o:p></SPAN></P>
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style="MARGIN-LEFT: 36pt; TEXT-INDENT: -18pt; mso-margin-top-alt: auto; mso-margin-bottom-alt: auto; tab-stops: list 36.0pt; mso-list: l0 level1 lfo2; mso-list-change: SGuy 20030510T1452"><![if !supportLists]><SPAN
lang=EN-US
style="FONT-SIZE: 10pt; FONT-FAMILY: Symbol; mso-bidi-font-family: Symbol; mso-fareast-language: ZH-CN; mso-fareast-font-family: Symbol; mso-bidi-font-size: 12.0pt"><SPAN
style="mso-list: Ignore">·<SPAN
style="FONT: 7pt 'Times New Roman'">
</SPAN></SPAN></SPAN><![endif]><U><SPAN lang=EN-US
style="FONT-FAMILY: 宋体; mso-bidi-font-family: 宋体; mso-fareast-language: ZH-CN"><A
href="http://www.gesoftfactory.com/developer/VnC.htm#裁剪体">裁剪体</A></SPAN></U><SPAN
lang=EN-US
style="FONT-FAMILY: 宋体; mso-bidi-font-family: 宋体; mso-fareast-language: ZH-CN"><o:p></o:p></SPAN></P>
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style="MARGIN-LEFT: 36pt; TEXT-INDENT: -18pt; mso-margin-top-alt: auto; mso-margin-bottom-alt: auto; tab-stops: list 36.0pt; mso-list: l0 level1 lfo2; mso-list-change: SGuy 20030510T1452"><![if !supportLists]><SPAN
lang=EN-US
style="FONT-SIZE: 10pt; FONT-FAMILY: Symbol; mso-bidi-font-family: Symbol; mso-fareast-language: ZH-CN; mso-fareast-font-family: Symbol; mso-bidi-font-size: 12.0pt"><SPAN
style="mso-list: Ignore">·<SPAN
style="FONT: 7pt 'Times New Roman'">
</SPAN></SPAN></SPAN><![endif]><U><SPAN lang=EN-US
style="FONT-FAMILY: 宋体; mso-bidi-font-family: 宋体; mso-fareast-language: ZH-CN"><A
href="http://www.gesoftfactory.com/developer/VnC.htm#视区缩放">视区缩放</A></SPAN></U><SPAN
lang=EN-US
style="FONT-FAMILY: 宋体; mso-bidi-font-family: 宋体; mso-fareast-language: ZH-CN"><o:p></o:p></SPAN></P>
<P class=MsoNormal
style="MARGIN-LEFT: 36pt; TEXT-INDENT: -18pt; mso-margin-top-alt: auto; mso-margin-bottom-alt: auto; tab-stops: list 36.0pt; mso-list: l0 level1 lfo2; mso-list-change: SGuy 20030510T1452"><![if !supportLists]><SPAN
lang=EN-US
style="FONT-SIZE: 10pt; FONT-FAMILY: Symbol; mso-bidi-font-family: Symbol; mso-fareast-language: ZH-CN; mso-fareast-font-family: Symbol; mso-bidi-font-size: 12.0pt"><SPAN
style="mso-list: Ignore">·<SPAN
style="FONT: 7pt 'Times New Roman'">
</SPAN></SPAN></SPAN><![endif]><U><SPAN lang=EN-US
style="FONT-FAMILY: 宋体; mso-bidi-font-family: 宋体; mso-fareast-language: ZH-CN"><A
href="http://www.gesoftfactory.com/developer/VnC.htm#视区的使用">视区的使用</A></SPAN></U><SPAN
lang=EN-US
style="FONT-FAMILY: 宋体; mso-bidi-font-family: 宋体; mso-fareast-language: ZH-CN"><o:p></o:p></SPAN></P>
<P class=MsoNormal
style="mso-margin-top-alt: auto; mso-margin-bottom-alt: auto"><SPAN lang=EN-US
style="FONT-FAMILY: 宋体; mso-bidi-font-family: 宋体; mso-fareast-language: ZH-CN">Direct3D通过给设备设置一系列的视区参数来实现裁剪。<o:p></o:p></SPAN></P>
<DIV class=MsoNormal style="TEXT-ALIGN: center" align=center><SPAN lang=EN-US
style="FONT-FAMILY: 宋体; mso-bidi-font-family: 宋体; mso-fareast-language: ZH-CN">
<HR align=center width="100%" SIZE=1>
</SPAN></DIV>
<P class=MsoNormal
style="mso-margin-top-alt: auto; mso-margin-bottom-alt: auto; mso-outline-level: 1"><A
name=视区矩形><B><SPAN
style="FONT-SIZE: 24pt; FONT-FAMILY: 宋体; mso-bidi-font-family: 宋体; mso-font-kerning: 18.0pt; mso-fareast-language: ZH-CN">视区矩形<SPAN
lang=EN-US><o:p></o:p></SPAN></SPAN></B></A></P><SPAN
style="mso-bookmark: 视区矩形"></SPAN>
<DIV class=MsoNormal style="TEXT-ALIGN: center" align=center><SPAN lang=EN-US
style="FONT-FAMILY: 宋体; mso-bidi-font-family: 宋体; mso-fareast-language: ZH-CN">
<HR align=center width="100%" SIZE=1>
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style="FONT-FAMILY: 宋体; mso-bidi-font-family: 宋体; mso-fareast-language: ZH-CN">C++应用程序通过使用<U>D3DVIEWPORT9</U>结构定义视区矩形。<B
style="mso-bidi-font-weight: normal">D3DVIEWPORT9</B>结构要配合以下<U>IDirect3DDevice9</U>接口暴露的视区操作方法一起使用。<o:p></o:p></SPAN></P>
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style="MARGIN-LEFT: 36pt; TEXT-INDENT: -18pt; mso-margin-top-alt: auto; mso-margin-bottom-alt: auto; tab-stops: list 36.0pt; mso-list: l3 level1 lfo3; mso-list-change: SGuy 20030510T1452"><![if !supportLists]><SPAN
lang=EN-US
style="FONT-SIZE: 10pt; FONT-FAMILY: Symbol; mso-bidi-font-family: Symbol; mso-fareast-language: ZH-CN; mso-fareast-font-family: Symbol; mso-bidi-font-size: 12.0pt"><SPAN
style="mso-list: Ignore">·<SPAN
style="FONT: 7pt 'Times New Roman'">
</SPAN></SPAN></SPAN><![endif]><U><SPAN lang=EN-US
style="COLOR: blue; FONT-FAMILY: 宋体; mso-bidi-font-family: 宋体; mso-fareast-language: ZH-CN">IDirect3DDevice9::GetViewport</SPAN></U><SPAN
lang=EN-US
style="FONT-FAMILY: 宋体; mso-bidi-font-family: 宋体; mso-fareast-language: ZH-CN">
<o:p></o:p></SPAN></P>
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style="MARGIN-LEFT: 36pt; TEXT-INDENT: -18pt; mso-margin-top-alt: auto; mso-margin-bottom-alt: auto; tab-stops: list 36.0pt; mso-list: l3 level1 lfo3; mso-list-change: SGuy 20030510T1452"><![if !supportLists]><SPAN
lang=EN-US
style="FONT-SIZE: 10pt; FONT-FAMILY: Symbol; mso-bidi-font-family: Symbol; mso-fareast-language: ZH-CN; mso-fareast-font-family: Symbol; mso-bidi-font-size: 12.0pt"><SPAN
style="mso-list: Ignore">·<SPAN
style="FONT: 7pt 'Times New Roman'">
</SPAN></SPAN></SPAN><![endif]><U><SPAN lang=EN-US
style="COLOR: blue; FONT-FAMILY: 宋体; mso-bidi-font-family: 宋体; mso-fareast-language: ZH-CN">IDirect3DDevice9::SetViewport</SPAN></U><SPAN
lang=EN-US
style="FONT-FAMILY: 宋体; mso-bidi-font-family: 宋体; mso-fareast-language: ZH-CN"><o:p></o:p></SPAN></P>
<P class=MsoNormal
style="mso-margin-top-alt: auto; mso-margin-bottom-alt: auto"><B
style="mso-bidi-font-weight: normal"><SPAN lang=EN-US
style="FONT-FAMILY: 宋体; mso-bidi-font-family: 宋体; mso-fareast-language: ZH-CN">D3DVIEWPORT9</SPAN></B><SPAN
style="FONT-FAMILY: 宋体; mso-bidi-font-family: 宋体; mso-fareast-language: ZH-CN">结构包含的四个成员——<B
style="mso-bidi-font-weight: normal"><SPAN lang=EN-US>X</SPAN></B>，<B
style="mso-bidi-font-weight: normal"><SPAN lang=EN-US>Y</SPAN></B>，<B
style="mso-bidi-font-weight: normal"><SPAN lang=EN-US>Width</SPAN></B>和<B
style="mso-bidi-font-weight: normal"><SPAN
lang=EN-US>Height</SPAN></B>——定义了渲染目标表面中的一块区域，场景将被渲染在该区域中。这些值对应于目标矩形，或视区矩形，如下图所示。<SPAN
lang=EN-US><o:p></o:p></SPAN></SPAN></P>
<P class=MsoNormal
style="mso-margin-top-alt: auto; mso-margin-bottom-alt: auto"><SPAN lang=EN-US
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<P class=MsoNormal
style="mso-margin-top-alt: auto; mso-margin-bottom-alt: auto"><SPAN
style="FONT-FAMILY: 宋体; mso-bidi-font-family: 宋体; mso-fareast-language: ZH-CN">应用程序给<B
style="mso-bidi-font-weight: normal"><SPAN
lang=EN-US>D3DVIEWPORT9</SPAN></B>结构的<B
style="mso-bidi-font-weight: normal"><SPAN lang=EN-US>X</SPAN></B>，<B
style="mso-bidi-font-weight: normal"><SPAN lang=EN-US>Y</SPAN></B>，<B
style="mso-bidi-font-weight: normal"><SPAN lang=EN-US>Width</SPAN></B>和<B
style="mso-bidi-font-weight: normal"><SPAN
lang=EN-US>Height</SPAN></B>成员指定的值是屏幕坐标，相对于渲染目标表面的左上角。该结构定义了两个附加成员（<B
style="mso-bidi-font-weight: normal"><SPAN lang=EN-US>MinZ</SPAN></B>和<B
style="mso-bidi-font-weight: normal"><SPAN
lang=EN-US>MaxZ</SPAN></B>），指出在这个深度范围内的场景会被渲染。<SPAN
lang=EN-US><o:p></o:p></SPAN></SPAN></P>
<P class=MsoNormal
style="mso-margin-top-alt: auto; mso-margin-bottom-alt: auto"><SPAN lang=EN-US
style="FONT-FAMILY: 宋体; mso-bidi-font-family: 宋体; mso-fareast-language: ZH-CN">Microsoft®
Direct3D®假设视区裁剪体在X方向上从-1.0到1.0，在Y方向上从1.0到-1.0。过去，这些是应用程序最常使用的设定。在投影变换过程中，应用程序可以在裁剪前调整纵横比。这项任务被涵盖在<U>投影变换</U>一节中。<o:p></o:p></SPAN></P>
<P class=MsoNormal><B style="mso-bidi-font-weight: normal"><SPAN
style="FONT-FAMILY: 宋体; mso-bidi-font-family: 宋体; mso-fareast-language: ZH-CN">注意<SPAN
lang=EN-US><SPAN style="mso-tab-count: 1">
</SPAN>D3DVIEWPORT9</SPAN></SPAN></B><SPAN
style="FONT-FAMILY: 宋体; mso-bidi-font-family: 宋体; mso-fareast-language: ZH-CN">结构的<B
style="mso-bidi-font-weight: normal"><SPAN lang=EN-US>MinZ</SPAN></B>和<B
style="mso-bidi-font-weight: normal"><SPAN
lang=EN-US>MaxZ</SPAN></B>成员指出在这个深度范围内的场景会被渲染，它们不用于裁剪。大多数应用程序把这两个成员设置为<SPAN
lang=EN-US>0.0和1.0，使系统能渲染深度缓存中全部范围的深度值。在一些情况下，应用程序可以通过使用其它的深度范围实现特殊效果。例如，要在游戏中显示提示（heads-up
display），应用程序可以将两个值都设为0.0，强制系统渲染场景中最前面的物体，或者也可以将它们都设为1.0，渲染总是在最后面的物体。<o:p></o:p></SPAN></SPAN></P>
<DIV class=MsoNormal style="TEXT-ALIGN: center" align=center><SPAN lang=EN-US
style="FONT-FAMILY: 宋体; mso-bidi-font-family: 宋体; mso-fareast-language: ZH-CN">
<HR align=center width="100%" SIZE=1>
</SPAN></DIV>
<P class=MsoNormal
style="mso-margin-top-alt: auto; mso-margin-bottom-alt: auto; mso-outline-level: 1"><A
name=视棱锥><B><SPAN
style="FONT-SIZE: 24pt; FONT-FAMILY: 宋体; mso-bidi-font-family: 宋体; mso-font-kerning: 18.0pt; mso-fareast-language: ZH-CN">视棱锥<SPAN
lang=EN-US><o:p></o:p></SPAN></SPAN></B></A></P><SPAN
style="mso-bookmark: 视棱锥"></SPAN>
<DIV class=MsoNormal style="TEXT-ALIGN: center" align=center><SPAN lang=EN-US
style="FONT-FAMILY: 宋体; mso-bidi-font-family: 宋体; mso-fareast-language: ZH-CN">
<HR align=center width="100%" SIZE=1>
</SPAN></DIV>
<P class=MsoNormal
style="mso-margin-top-alt: auto; mso-margin-bottom-alt: auto"><SPAN
style="FONT-FAMILY: 宋体; mso-bidi-font-family: 宋体; mso-fareast-language: ZH-CN">视棱锥是场景中的三维区域，相对于视区的摄像机。区域的形状会影响到建模如何从摄像机空间投影到屏幕。最普通的投影类型，透视投影，是造成离摄像机近的物体显得比远处物体大的原因。对于透视变换，视棱锥可以被想象成一个金字塔，摄像机被放在顶端。这个金字塔分别被前后裁剪平面截取。金字塔中部位于前后裁剪平面之间的区域就是视棱锥。物体只有在这个区域中时才是可见的。<SPAN
lang=EN-US><o:p></o:p></SPAN></SPAN></P>
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