How to call glPointSize() (or the SceneKit equivalent) when making custom geometries using SceneKit and SCNGeometryPrimitiveTypePoint

Question

I'm writing an iOS app that renders a pointcloud in SceneKit using a custom geometry. This post was super helpful in getting me there (though I translated this to Objective-C), as was David Rönnqvist's book 3D Graphics with SceneKit (see chapter on custom geometries). The code works fine, but I'd like to make the points render at a larger point size - at the moment the points are super tiny.

According to the OpenGL docs, you can do this by calling glPointSize(). From what I understand, SceneKit is built on top of OpenGL so I'm hoping there is a way to access this function or do the equivalent using SceneKit. Any suggestions would be much appreciated!

My code is below. I've also posted a small example app on bitbucket accessible here.

// set the number of points
NSUInteger numPoints = 10000;

// set the max distance points
int randomPosUL = 2;
int scaleFactor = 10000; // because I want decimal points
                         // but am getting random values using arc4random_uniform

PointcloudVertex pointcloudVertices[numPoints];

for (NSUInteger i = 0; i < numPoints; i++) {

    PointcloudVertex vertex;

    float x = (float)(arc4random_uniform(randomPosUL * 2 * scaleFactor));
    float y = (float)(arc4random_uniform(randomPosUL * 2 * scaleFactor));
    float z = (float)(arc4random_uniform(randomPosUL * 2 * scaleFactor));

    vertex.x = (x - randomPosUL * scaleFactor) / scaleFactor;
    vertex.y = (y - randomPosUL * scaleFactor) / scaleFactor;
    vertex.z = (z - randomPosUL * scaleFactor) / scaleFactor;

    vertex.r = arc4random_uniform(255) / 255.0;
    vertex.g = arc4random_uniform(255) / 255.0;
    vertex.b = arc4random_uniform(255) / 255.0;

    pointcloudVertices[i] = vertex;

    //        NSLog(@"adding vertex #%lu with position - x: %.3f y: %.3f z: %.3f | color - r:%.3f g: %.3f b: %.3f",
    //              (long unsigned)i,
    //              vertex.x,
    //              vertex.y,
    //              vertex.z,
    //              vertex.r,
    //              vertex.g,
    //              vertex.b);
}

// convert array to point cloud data (position and color)
NSData *pointcloudData = [NSData dataWithBytes:&pointcloudVertices length:sizeof(pointcloudVertices)];

// create vertex source
SCNGeometrySource *vertexSource = [SCNGeometrySource geometrySourceWithData:pointcloudData
                                                                   semantic:SCNGeometrySourceSemanticVertex
                                                                vectorCount:numPoints
                                                            floatComponents:YES
                                                        componentsPerVector:3
                                                          bytesPerComponent:sizeof(float)
                                                                 dataOffset:0
                                                                 dataStride:sizeof(PointcloudVertex)];

// create color source
SCNGeometrySource *colorSource = [SCNGeometrySource geometrySourceWithData:pointcloudData
                                                                  semantic:SCNGeometrySourceSemanticColor
                                                               vectorCount:numPoints
                                                           floatComponents:YES
                                                       componentsPerVector:3
                                                         bytesPerComponent:sizeof(float)
                                                                dataOffset:sizeof(float) * 3
                                                                dataStride:sizeof(PointcloudVertex)];

// create element
SCNGeometryElement *element = [SCNGeometryElement geometryElementWithData:nil
                                                            primitiveType:SCNGeometryPrimitiveTypePoint
                                                           primitiveCount:numPoints
                                                            bytesPerIndex:sizeof(int)];

// create geometry
SCNGeometry *pointcloudGeometry = [SCNGeometry geometryWithSources:@[ vertexSource, colorSource ] elements:@[ element]];

// add pointcloud to scene
SCNNode *pointcloudNode = [SCNNode nodeWithGeometry:pointcloudGeometry];
[self.myView.scene.rootNode addChildNode:pointcloudNode];

Xartec Xartec · Accepted Answer · 2017-01-16T04:40:44

I was looking into rendering point clouds in ios myself and found a solution on twitter, by a "vade", and figured I post it here for others:

ProTip: SceneKit shader modifiers are useful:

mat.shaderModifiers = @{SCNShaderModifierEntryPointGeometry : @"gl_PointSize = 16.0;"};

How to call glPointSize() (or the SceneKit equivalent) when making custom geometries using SceneKit and SCNGeometryPrimitiveTypePoint

1 Answers