ios - 如何在SCNSphere对象上应用脉冲效果？

我想在SCNSphere对象上应用脉冲效果，对此有谁能帮助我。

Pulse effect



提前致谢。

最佳答案

我在其中一个应用程序中具有类似的效果(请参见下文)，并使用了SceneKit着色器修改器。



这是一些可能有用的示例代码。

 let boxNode = SCNNode(geometry: SCNBox(width: 1.0, height: 1.0, length: 1.0, chamferRadius: 0))
 boxNode.geometry?.firstMaterial?.diffuse.contents = UIColor.red
 scene.rootNode.addChildNode(boxNode)

 let pulseSize:CGFloat = 5.0
 let pulsePlane = SCNPlane(width: pulseSize, height: pulseSize)
 pulsePlane.firstMaterial?.isDoubleSided = true
 pulsePlane.firstMaterial?.diffuse.contents = UIColor.blue
 let pulseNode = SCNNode(geometry: pulsePlane)

 let pulseShaderModifier =
 "#pragma transparent; \n" +
 "vec4 originalColour = _surface.diffuse; \n" +
 "vec4 transformed_position = u_inverseModelTransform * u_inverseViewTransform * vec4(_surface.position, 1.0); \n" +
 "vec2 xy = vec2(transformed_position.x, transformed_position.y); \n" +
 "float xyLength = length(xy); \n" +
 "float xyLengthNormalised = xyLength/" + String(describing: pulseSize / 2) + "; \n" +
 "float speedFactor = 1.5; \n" +
 "float maxDist = fmod(u_time, speedFactor) / speedFactor; \n" +
 "float distbasedalpha = step(maxDist, xyLengthNormalised); \n" +
 "distbasedalpha = max(distbasedalpha, maxDist); \n" +
 "_surface.diffuse = mix(originalColour, vec4(0.0), distbasedalpha);"

 pulsePlane.firstMaterial?.shaderModifiers = [SCNShaderModifierEntryPoint.surface:pulseShaderModifier]
 boxNode.addChildNode(pulseNode)

包含红色框(boxNode)仅用于上下文。

脉冲节点由SCNPlane组成，可通过SceneKit的表面着色器修改器修改片段着色器。如果注释掉设置shader修改器的代码，则将按预期看到一个平坦的蓝色正方形。

为着色器修改器的曲面入口点指定的代码被注入SceneKit使用的片段着色器中。这意味着您正在使用像素的屏幕空间。着色器修改器的前几行使用逆模型和视图变换将屏幕空间坐标转换回模型空间坐标。

计算每个与平面中心(在模型空间中)的像素距离xyLength。然后将其标准化为“脉冲平面” xyLengthNormalised的总大小。时间上的模运算用于获得脉冲效果。您可以将其切换到sin函数，以获取先进先出型脉冲。我们使用mod操作的结果来确定哪些像素应该是透明的。

平面与红色框一起旋转，因为它是该框的子节点。您可以通过添加约束来覆盖此行为，如下所示。我曾经研究过约束条件，因为我个人从未对SCNBillboardConstraint取得太大的成功。

let pulseNodeConstraint = SCNLookAtConstraint(target: cameraNode)
pulseNode.constraints = [pulseNodeConstraint]

最终结果



对于那些喜欢Objective-C的人...

SCNNode *boxNode = [SCNNode nodeWithGeometry:[SCNBox boxWithWidth:1.0 height:1.0 length:1.0 chamferRadius:0.0]];
boxNode.geometry.firstMaterial.diffuse.contents = [UIColor redColor];
[scene.rootNode addChildNode:boxNode];

CGFloat pulseSize = 5.0;
SCNPlane *pulsePlane = [SCNPlane planeWithWidth:pulseSize height:pulseSize];
[pulsePlane.firstMaterial setDoubleSided:true];
pulsePlane.firstMaterial.diffuse.contents = [UIColor blueColor];
SCNNode *pulseNode = [SCNNode nodeWithGeometry:pulsePlane];

NSString *pulseShaderModifier = [NSString stringWithFormat:
@"#pragma transparent; \n"
"vec4 originalColour = _surface.diffuse; \n"
"vec4 transformed_position = u_inverseModelTransform * u_inverseViewTransform * vec4(_surface.position, 1.0); \n"
"vec2 xy = vec2(transformed_position.x, transformed_position.y); \n"
"float xyLength = length(xy); \n"
"float xyLengthNormalised = xyLength/%f; \n"
"float speedFactor = 1.5; \n"
"float maxDist = fmod(u_time, speedFactor) / speedFactor; \n"
"float distbasedalpha = step(maxDist, xyLengthNormalised); \n"
"distbasedalpha = max(distbasedalpha, maxDist); \n"
"_surface.diffuse = mix(originalColour, vec4(0.0), distbasedalpha);", pulseSize/2.0];

NSDictionary *smdict = [NSDictionary dictionaryWithObject:pulseShaderModifier forKey:SCNShaderModifierEntryPointSurface];
[pulsePlane.firstMaterial setShaderModifiers:smdict];

[boxNode addChildNode:pulseNode];

SCNLookAtConstraint *pulseNodeConstraint = [SCNLookAtConstraint lookAtConstraintWithTarget:cameraNode];
NSArray *constraints = [NSArray arrayWithObject:pulseNodeConstraint];
[pulseNode setConstraints:constraints];

关于ios - 如何在SCNSphere对象上应用脉冲效果？，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/42664563/