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HomeWeb Front-endH5 Tutorialopengl/webgl 可以部分重绘吗?

我是webgl的初学者,在学习过程中发现教程中讲解 webgl 动画的时候,基本都是清除屏幕,然后应用变换,重新绘制这样的过程来达到动起来的效果。 但是我想,如果在一个非常复杂的场景中,只有一个很小的部分在移动,那么是否可以只绘制这很小的一部分不用全部的重新绘制呢?

回复内容:

实践上通常没太大意义。因为对于一个典型的3D场景,很多影响是全局的。比如一个物体的投影,很可能投到离得很远的另一个物体上。再比如运动模糊、ambient occlusion这类二维特效,也得是在整个场景渲染到二维的基础上。你只刷屏幕上面的一个块,就“不对”了。
实际上,3D场景的剪裁,通常在场景图上完成,而不是在屏幕空间上搞。 用scissor test,你就可以只clear一部分,只画那块区域的物体,再配合EGL_NV_post_sub_buffer,就可以只swap一部分。

但是实际使用中,你仍会发现这么做没意义,几乎所有时候你都会需要刷全屏。 如上面大家所说的 scissor test 可以做这个。不过一般3d场景用这个意义不大。因为你这个移动的小物体,可能影响到其他物体或者全局绘制的物体。这种情况下还是要重绘的。

但在特殊的一些场景上可以用到:
1 比如那种3d编辑器的左视图,上视图,下视图等等。在不同的区域显示不同的视角。
2 立体3D 需要绘制左眼/右眼 区域。其实和1类似。
3 3D UI,就是基于OpenGL/ES 接口做的 2D UI效果。比如安卓UI系统/一些电视上Launcher等等。 你说的这种情况在远程绘制的时候有应用。
比如一个类似足球游戏的场景,其实显示端不太关注观众台,这样观众台的信息是不用每帧都传输的(只需要第一帧的时候传输背景,之后可以若干帧传输一次,或者再也不传输)。

但是我说的这个应用和你所描述的是不一样的,因为远程绘制的瓶颈可能是网络,而不是绘制时间。 可以的,渲染视频的时候就这么做过。
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