OS X上的SceneKit包含数千个对象

Question

我正在学习本教程:http://blog.bignerdranch.com/754-scenekit-in-mountain-lion/

我对使用Scene Kit感兴趣,但我的场景可能有数千个球体.要对Scene Kit进行压力测试,我试过这个:

SCNSphere *sphere = [SCNSphere sphereWithRadius:0.5];
for (int i=0; i<10; i++) {
    for(int j=0; j<10; j++){
        for(int k=0; k<10; k++){
            SCNNode *myNode = [SCNNode nodeWithGeometry:sphere];
            myNode.position = SCNVector3Make(i,j,k);
            [root addChildNode:myNode];
        }
    }
}

这适用于1000球(10 ^ 3),但是对于1,000,000个球(100 ^ 3)而言失败(也许不足为奇).我不介意不能使用一百万个球体,但我想弄清楚明智的上限是什么(5,000？15,000？)以及如何增加它.

我该怎么做才能缓解这种情况？例如,我已经尝试了sphere.segmentCount = 3,虽然这加快了渲染速度,但它对内存使用没有太大影响,我怀疑这是限制因素.

此外,似乎没有SCNPoint类.我在考虑切换到仅在球体数量太高时显示一个点,但我无法从SceneKit文档中看到如何显示一个简单的点 - 我能看到的最简单的是一个三角形.

任何帮助深表感谢.

编辑: @toyos建议将SCNSphere对象合并到单个SCNGeometry对象中(前提是它们不需要独立动画,但它们不需要),但我找不到一种简单的方法来执行此操作.

SCNGeometry是使用此处[SCNGeometry geometryWithSources:(* NSArray)sources geometryWithElements:(* NSArray) elements]记录的创建的,但我不清楚如何从我的领域创建一个对象.SCNGeometry

例如,对于单个球体,我可以看到使用sphere.geometryElementCount获取元素的数量,然后使用它来填充数组,使用[sphere geometryElementAtIndex:(NSInteger)elementIndex]它可以给我元素,但我不知道如何获得"源"(或者它们甚至是什么)是).获取几何源的方法是[sphere geometrySourcesForSemantic:(NSString*) semantic],但这个语义字符串是什么？(它意味着是"法线"还是"顶点"还是其他的东西？文档非常有用地说语义是"几何源的语义值."而没有说出语义的可能值是什么)

这只是一个单一的球体,这将是毫无意义的(因为SCNSphere它只是一个SCNGeometry无论如何的子类),所以现在我必须添加多个球体.那么在将它们添加到我的SCNGeometry对象时,我是否必须手动转换球体的顶点？

我只是想弄清楚最明智的方法来做到这一点.

Answer 1

语义字符串是SCNGeometrySourceSemanticVertex | Normal | Texcoord ...

对于多个球体,答案是肯定的,您必须在展平前使用当前节点变换变换顶点/法线.

下面是一个简化的例子(即它只支持合并"输入"的子项,如果它们都具有相同的几何)

- (SCNNode *) flattenNodeHierarchy:(SCNNode *) input
{
    SCNNode *result = [SCNNode node];

    NSUInteger nodeCount = [[input childNodes] count];
    if(nodeCount > 0){
    SCNNode *node = [[input childNodes] objectAtIndex:0];

        NSArray *vertexArray = [node.geometry geometrySourcesForSemantic:SCNGeometrySourceSemanticVertex];
        SCNGeometrySource *vertex = [vertexArray objectAtIndex:0];

        SCNGeometryElement *element = [node.geometry geometryElementAtIndex:0]; //todo: support multiple elements
        NSUInteger primitiveCount = element.primitiveCount;
        NSUInteger newPrimitiveCount = primitiveCount * nodeCount;
        size_t elementBufferLength = newPrimitiveCount * 3 * sizeof(int); //nTriangle x 3 vertex * size of int
        int* elementBuffer = (int*)malloc(elementBufferLength);

        /* simple case: here we consider that all the objects to flatten are the same
         In the regular case we should iterate on every geometry and accumulate the number of vertex/triangles etc...*/

        NSUInteger vertexCount = [vertex vectorCount];
        NSUInteger newVertexCount = vertexCount * nodeCount;

        SCNVector3 *newVertex = malloc(sizeof(SCNVector3) * newVertexCount);        
        SCNVector3 *newNormal = malloc(sizeof(SCNVector3) * newVertexCount); //assume same number of normal/vertex

        //fill
        NSUInteger vertexFillIndex = 0;
        NSUInteger primitiveFillIndex = 0;
        for(NSUInteger index=0; index< nodeCount; index++){
            NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];

            node = [[input childNodes] objectAtIndex:index];

            NSArray *vertexArray = [node.geometry geometrySourcesForSemantic:SCNGeometrySourceSemanticVertex];
            NSArray *normalArray = [node.geometry geometrySourcesForSemantic:SCNGeometrySourceSemanticNormal];
            SCNGeometrySource *vertex = [vertexArray objectAtIndex:0];
            SCNGeometrySource *normals = [normalArray objectAtIndex:0];

            if([vertex bytesPerComponent] != sizeof(float)){
                NSLog(@"todo: support other byte per component");
                continue;
            }

            float *vertexBuffer = (float *)[[vertex data] bytes];
            float *normalBuffer = (float *)[[normals data] bytes];

            CATransform3D t = [node transform];
            GLKMatrix4 matrix = MyGLKMatrix4FromCATransform3D(t);

            //append source
            for(NSUInteger vIndex = 0; vIndex < vertexCount; vIndex++, vertexFillIndex++){
                GLKVector3 v = GLKVector3Make(vertexBuffer[vIndex * 3], vertexBuffer[vIndex * 3+1], vertexBuffer[vIndex * 3 + 2]);
                GLKVector3 n = GLKVector3Make(normalBuffer[vIndex * 3], normalBuffer[vIndex * 3+1], normalBuffer[vIndex * 3 + 2]);

                //transform
                v = GLKMatrix4MultiplyVector3WithTranslation(matrix, v);
                n = GLKMatrix4MultiplyVector3(matrix, n);

                newVertex[vertexFillIndex] = SCNVector3Make(v.x, v.y, v.z);
                newNormal[vertexFillIndex] = SCNVector3Make(n.x, n.y, n.z);
            }

            //append elements
            //here we assume that all elements are SCNGeometryPrimitiveTypeTriangles
            SCNGeometryElement *element = [node.geometry geometryElementAtIndex:0];
            const void *inputPrimitive = [element.data bytes];
            size_t bpi = element.bytesPerIndex;

            NSUInteger offset = index * vertexCount;

            for(NSUInteger pIndex = 0; pIndex < primitiveCount; pIndex++, primitiveFillIndex+=3){                
                elementBuffer[primitiveFillIndex] = offset + _getIndex(inputPrimitive, bpi, pIndex*3);
                elementBuffer[primitiveFillIndex+1] = offset + _getIndex(inputPrimitive, bpi, pIndex*3+1);
                elementBuffer[primitiveFillIndex+2] = offset + _getIndex(inputPrimitive, bpi, pIndex*3+2);
            }

            [pool drain];
        }

        NSArray *sources = @[[SCNGeometrySource geometrySourceWithVertices:newVertex count:newVertexCount],
                             [SCNGeometrySource geometrySourceWithNormals:newNormal count:newVertexCount]];

        NSData *newElementData = [NSMutableData dataWithBytesNoCopy:elementBuffer length:elementBufferLength freeWhenDone:YES];
        NSArray *elements = @[[SCNGeometryElement geometryElementWithData:newElementData
                                                            primitiveType:SCNGeometryPrimitiveTypeTriangles
                                                           primitiveCount:newPrimitiveCount bytesPerIndex:sizeof(int)]];

        result.geometry = [SCNGeometry geometryWithSources:sources elements:elements];

        //cleanup
        free(newVertex);
        free(newNormal);
    }

    return result;
}

//helpers:
GLKMatrix4 MyGLKMatrix4FromCATransform3D(CATransform3D transform) {
    GLKMatrix4 m = {{transform.m11, transform.m12, transform.m13, transform.m14,
        transform.m21, transform.m22, transform.m23, transform.m24,
        transform.m31, transform.m32, transform.m33, transform.m34,
        transform.m41, transform.m42, transform.m43, transform.m44}};
    return m;
}



GLKVector3 MySCNVector3ToGLKVector3(SCNVector3 vector) {
    GLKVector3 v = {{vector.x, vector.y, vector.z}};
    return v;
}