opengl - 使用 SceneKit 自定义裁剪平面

Question

使用 SceneKit 时是否可以创建自定义裁剪平面？由于您可以提供自己的着色器，因此我唯一需要做的就是以某种方式启用 GL_CLIP_DISTANCE0。这是可能的还是我必须坚持使用较低级别的库？

编辑:

我尝试使用渲染器委托(delegate)启用 GL 状态 GL_CLIP_DISTANCE0，但没有效果。这是相关代码部分:

class GameViewController: NSViewController, SCNSceneRendererDelegate {

 @IBOutlet weak var gameView: GameView!

 override func awakeFromNib() {
   let attrs: [Int] = [
     NSOpenGLPFADoubleBuffer,
     NSOpenGLPFADepthSize, 24,
     NSOpenGLPFAOpenGLProfile,
     NSOpenGLProfileVersion3_2Core,
     0
   ]

   let pixelFormat: NSOpenGLPixelFormat = NSOpenGLPixelFormat(attributes: UnsafePointer<NSOpenGLPixelFormatAttribute>(attrs))

   gameView.pixelFormat = pixelFormat

   let scene = SCNScene()      
   let obj = SCNSphere(radius: 1.0)
   obj.shaderModifiers = [SCNShaderModifierEntryPointGeometry: "gl_CLipDistance[0] = 0.0;"]
   let objNode = SCNNode(geometry: obj)
   scene.rootNode.addChildNode(objNode)

   // ... create camera and lights ...

   // set renderer delegate
   self.gameView.delegate = self

   // set the scene to the view
   self.gameView!.scene = scene      
   self.gameView!.backgroundColor = NSColor.blackColor()
 }

 func renderer(aRenderer: SCNSceneRenderer, updateAtTime time: NSTimeInterval) {
  glEnable(GLenum(GL_CLIP_DISTANCE0))
 }
}

无论我尝试什么，我都会收到以下错误:

SceneKit: error,   2: uniform mat4 u_normalTransform;
SceneKit: error,   3: uniform mat4 u_projectionTransform;
SceneKit: error,   4: uniform mat4 u_modelViewTransform;
SceneKit: error,   5: // In model space, must stay in it
SceneKit: error,   6: struct SCNShaderGeometry
SceneKit: error,   7: {
SceneKit: error,   8:   vec4 position;
SceneKit: error,   9:   vec3 normal;
SceneKit: error,  10:   vec4 tangent;
SceneKit: error,  11:   vec4 color;
SceneKit: error,  12:   vec2 texcoords[8]; // MAX_UV
SceneKit: error,  13: } _geometry;
SceneKit: error,  14: struct SCNShaderSurface
SceneKit: error,  15: {
SceneKit: error,  16:   vec3 view; // in view space
SceneKit: error,  17:   vec3 position; // in view space
SceneKit: error,  18:   vec3 normal; // in view space
SceneKit: error,  19:   vec3 tangent; // in view space
SceneKit: error,  20:   vec3 bitangent; // in view space
SceneKit: error,  21:   float shininess;
SceneKit: error,  22:   float fresnel;
SceneKit: error,  23:   vec3 _normalTS; // UNDOCUMENTED in tangent space
SceneKit: error,  24:   vec4 diffuse;
SceneKit: error,  25: } _surface;
SceneKit: error,  26: // Attributes
SceneKit: error,  27: attribute vec4 a_position;
SceneKit: error,  28: attribute vec3 a_normal;
SceneKit: error,  29: // Varyings
SceneKit: error,  30: varying vec3 v_position;
SceneKit: error,  31: varying vec3 v_normal;
SceneKit: error,  32: void main(void)
SceneKit: error,  33: {
SceneKit: error,  34:   _geometry.position = a_position;
SceneKit: error,  35:   _geometry.normal = a_normal;
SceneKit: error,  36:   gl_CLipDistance[0] = 0.0;
SceneKit: error,  37:   // Transform the geometry elements in view space
SceneKit: error,  38:   _surface.position = (u_modelViewTransform * _geometry.position).xyz;
SceneKit: error,  39:   _surface.normal = normalize(mat3(u_normalTransform) * _geometry.normal);
SceneKit: error,  40:   //if USE_VIEW is 2 we may also need to set _surface.view. todo: make USE_VIEW a mask
SceneKit: error,  41:   v_position = _surface.position;
SceneKit: error,  42:   v_normal = _surface.normal;
SceneKit: error,  43:     
SceneKit: error,  44:   // this means that the geometry are still in model space
SceneKit: error,  45:   gl_Position = u_projectionTransform * vec4(_surface.position, 1.);
SceneKit: error,  46: }
SceneKit: error,  47: 
SceneKit: error, failed to link program: ERROR: 0:36: Use of undeclared identifier 'gl_CLipDistance'

我做错了什么或者“gl_ClipDistance”在 SceneKit 使用的 OpenGL 版本中根本不可用吗？

Answer 1

如果您想在 SceneKit 渲染场景之前启用某些 GL 状态，请使用 scene renderer delegate 。在 renderer:willRenderScene:atTime: 方法中，您可以 glEnable 自定义着色器所依赖的任何状态。