使用着色器修改器在SceneKit中为纹理设置动画会随着时间的推移导致抖动纹理 [英] Using shader modifiers to animate texture in SceneKit leads to jittery textures over time

问题描述

我正在为SceneKit for iOS编写场景。

I'm writing a scene in SceneKit for iOS.

我正在尝试使用精灵表格将纹理应用于对象。我使用以下代码遍历该表中的图像：

I'm trying to apply a texture to an object using a sprite sheet. I iterate through the images in that sheet with this code:

happyMaterial = [SCNMaterial new];
happyMaterial.diffuse.contents = happyImage;
happyMaterial.diffuse.wrapS = SCNWrapModeRepeat;
happyMaterial.diffuse.wrapT = SCNWrapModeRepeat;
happyMaterial.shaderModifiers = @{ SCNShaderModifierEntryPointGeometry : @"_geometry.texcoords[0] = vec2((_geometry.texcoords[0].x+floor(u_time*30.0))/10.0, (_geometry.texcoords[0].y+floor(u_time*30.0/10.0))/7.0);" };

一切都很好。除了随着时间的推移，纹理开始在其中产生随机抖动，特别是沿着x轴。

All is good. Except over time, the texture starts to get random jitteriness in it, especially along the x-axis.

有人提到它可能是因为浮点精度问题， 但我不确定如何诊断或修复此问题。

Someone mentioned it could be because of "floating-point precision issues," but I'm not sure how to diagnose or fix this.

另外：我不确定如何从着色器代码中记录数据。能够查看像u_time这样的变量并查看到底发生了什么真是太棒了。

Also: I'm not sure how to log data from the shader code. Would be awesome to be able to look into variables like "u_time" and see exactly what's going on.

推荐答案

这绝对是浮动的点精度问题。你应该尝试在（u_time * 30.0）上进行模数运算，以便它在合理的范围内循环。

It's definitely a floating point precision issue. you should probably try to do a modulo on (u_time*30.0) so that it loops within a reasonable range.

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