含义和glPolygonOffset因素参数的用法 [英] Meaning and usage of the factor parameter in glPolygonOffset

问题描述

我难以理解的第一个参数的含义 glPolygonOffset 功能。

I am having difficulty understanding the meaning of the first parameter in glPolygonOffset function.

void glPolygonOffset(GLfloat  factor, GLfloat units);

的官方文档说系数

指定用于创建一个可变深度为每个多边形偏移的比例因子

Specifies a scale factor that is used to create a variable depth offset for each polygon.

和

它是从相应的顶点的深度值内插后的各片段的深度值将被抵消。偏移的值是因子×DZ + R×单元，其中DZ为相对于多边形的屏幕区域深度的变化的测定，而r是保证产生可解析为一个给定的偏移量的值最小实施

each fragment's depth value will be offset after it is interpolated from the depth values of the appropriate vertices. The value of the offset is factor × DZ + r × units , where DZ is a measurement of the change in depth relative to the screen area of the polygon, and r is the smallest value that is guaranteed to produce a resolvable offset for a given implementation.

我明白了什么研究和单元是。我不明白的是什么 DZ 是，即什么是由深度价值的多边形的屏幕面积变化的测量，为什么会意味着我以往任何时候都需要系数设置为0以外的任何

I understand what r and unit are. What I don't understand is what DZ is, i.e. what is meant by the "measurement of the change in depth value to the screen area of the polygon" and why would I ever need to set factor to anything other than 0.

如果我希望我的线框，以抵消所有我需要的是添加/ substact几个单位/从深度值，不是吗？有什么因素参数的意义，目的和使用实例（和文件中提到的DZ）？

If i want my wireframe to be offset all I need is to add/substact a couple of units to/from the depth value, don't I? What's the meaning, purpose and usage example of the factor parameter (and the DZ mentioned in the document)?

推荐答案

我必须在这里承认一些无知，但我发现的这篇文章这也解释了它。他们说：

I have to admit some ignorance here, but I found this article which explains it. They say:

要实现突出固体物体的一个很好的渲染没有视觉假象，你可以添加一个正偏移到实体对象（推离你而去）或负偏移线框（向外拉出）。最大的问题是：多少偏移量是够了吗？不幸的是，要求的偏差取决于各种因素，包括每个多边形的深度斜率和在线框的线的宽度。

To achieve a nice rendering of the highlighted solid object without visual artifacts, you can either add a positive offset to the solid object (push it away from you) or a negative offset to the wireframe (pull it towards you). The big question is: "How much offset is enough?" Unfortunately, the offset required depends upon various factors, including the depth slope of each polygon and the width of the lines in the wireframe.

他们然后解释深度坡度是这样的：

They then explain the depth slope this way:

深度斜率是由在x或y坐标的变化除以在Z（深度）值的变化，因为你遍历多边形。深度值是在窗口坐标，钳位到范围[0,1]。为了估计多边形（偏移式米）的最大深度坡度，使用这个公式：M = {最大值| delV /德尔斯|，| delV / DELT |}。 （其中，德尔是一个偏导数）

The depth slope is the change in z (depth) values divided by the change in either x or y coordinates, as you traverse a polygon. The depth values are in window coordinates, clamped to the range [0, 1]. To estimate the maximum depth slope of a polygon (m in the offset equation), use this formula: m = max {|delV / delS|,|delV / delT|}. (where del is a partial derivative)

因此​​，他们得出这样的结论：

So they conclude that:

有关的是平行于所述近端和远端剪切平面多边形，深度斜率为零。 [...]对于多边形是在一个大的角度向剪切平面，深度斜率可以比零显著更大，而较大的，可能需要偏移。小，无零因子，如0.75或1.0的值，可能足以产生不同深度的价值观和消除不愉快的视觉假象。

For polygons that are parallel to the near and far clipping planes, the depth slope is zero. [...] For polygons that are at a great angle to the clipping planes, the depth slope can be significantly greater than zero, and a larger offset may be needed. Small, non-zero values for factor, such as 0.75 or 1.0, are probably enough to generate distinct depth values and eliminate the unpleasant visual artifacts.

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