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English

Overview

This guide describes the process of using alpha-blended decals to create broken concrete pieces and building ruins of high visual quality.

In most games destroyed walls and other buildings structures are done by simply cutting into the geometry and applying a tiling concrete texture to the broken area.

While it is performance-effective and simple to do this, the disadvantage of this technique is that you are left with a very visible and sharp seam between the two materials. It is a more work-intensive but visually better solution to use decals with alpha-blending in order to avoid these seams.

Info
While both solutions use two material IDs, the new technique introduces additional overdraw through the alpha-blending and thus is the more expensive method.

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Traditional Technique

Note the sharp seam between the two materials (marked in orange).

Alpha-Blended Decals

Note the more believable transition between the two materials (marked in orange).

The normal map used for this decal:

Example for "chipped-off" pieces using alphablend decals:

The normal map used for this decal:

Using These Decals in a 3D Application

  • Add an extra geometry element for the broken edge.
  • Extrude the border edges of this element inwards so they overlap the other material.
  • Adjust the UV mapping of the element to create the overlap.

Here you can see the extra geometry element following the edge of your broken piece of building:

Here you can see how the UV mapping must be adjusted to create a convincing overlap of the two materials:

Use the chipped-off looking edge decals by

  • Duplicating the geometry of whichever edge you want to use them on
  • Cutting out the part where the decal will be visible
  • Adjusting the UV mapping to show the decal in the right position

Illustration of these steps:

Another example:

For the best results, use the low-res geometry you used for rendering the normal map, snap them on the edge of the object you are working on, and cut its shape out of the solid block using the knife tool together with vertex snapping.

Using this method, you will also have the correct silhouette.

 

Excerpt
hiddentrue
This guide describes the process of using alpha-blended decals to create broken concrete pieces and building ruins with a high visual quality.
Chinese

对被破坏的结构使用贴花

本指南描述使用 alpha 混合的贴花创建破坏的混凝土片段以及建立高质量视觉效果废墟的过程。

在大多数游戏中,被破坏的墙壁和其他构建结构由简单地切成几何体并将重复拼贴混凝土纹理应用到破损区域而得到的。

这是高效简单的做法,但是此技术的缺点是会在两个材质之间留下明显可见且尖锐的接缝。为避免这些接缝,最好的解决方案是使用 alpha 混合的贴花,虽然工作量很大,但是能得到很好的视觉效果。

*注:*两种解决方案都需要两种材质 ID,新的技术通过 alpha 混合引入了额外的重复绘制,因此此方法更加昂贵。

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传统技术

注意两种材质之间尖锐的接缝(用橙色标记)。

Alpha 混合的贴花

注意两种材质之间更加可信的过渡(用橙色标记)。

适用于此贴花的法线贴图:

使用 alpha 混合的贴花的“横断面”片段的示例:

适用于此贴花的法线贴图:

在 3D 应用程序中使用这些贴花

本图中您能看到沿着破损片段的边缘添加的额外几何体元素:

本图中可以看到应该怎样调整 UV 映射以在两种材质上创建令人信服的重叠:

通过下列方法使用横断面外观的边缘贴花

用于说明上述步骤的插图:

另一个示例:

为获得最佳效果,请使用低分辨率的几何体,使用法线贴图渲染,并将它们在您正在工作的对象边缘上对齐,使用刻刀工具和顶点对齐将超出实体块的形状切除。

使用此方法就能得到正确的轮廓。