三 JS 从合并几何中删除 BOX 几何

Question

我有 100k+ 个盒子被添加到合并的几何图形中。我需要偶尔从这个合并的几何图形中删除一些几何图形。我可以按每个立方体 108 或 72 个顶点的步长循环位置属性以提取这些框的位置还是合并也合并顶点？

function blockCubeAlter(grid, blockModel) {

        function getGridElevation(n, e, grid) {
            var y_grid = Math.floor((grid.metaData.yMax - n) / grid.metaData.yStep) + 1;
            var x_grid = Math.floor((e - grid.metaData.xMin) / grid.metaData.xStep);

            var array_pos = Math.round(y_grid * (grid.metaData.nCol + 1) + x_grid);
            return isNaN(grid.elevations[array_pos]) ? Infinity : grid.elevations[array_pos];
        }

        var tmpBox = new THREE.BoxBufferGeometry(blockModel.x_step, blockModel.y_step, 2);

        var myBlock = scene.getObjectByName('blockModel');

        var pointsPerVertex = 3,
            vertexPerFace = 4,// this might be 3 triangles?
            facePerSide = 1, // this might be 2 triangles per face?
            sidePerBox = 6;

        var pointsPerCube = pointsPerVertex * vertexPerFace * facePerSide * sidePerBox;
        for (var i = 0, j = myBlock.geometry.attributes.position.array.length; i < j; i += pointsPerCube) {
            var above = false,
                below = false;

            for (var k = i; k < i + pointsPerCube; k += pointsPerVertex) {
                var n = myBlock.geometry.attributes.position.array[k + 1];
                var e = myBlock.geometry.attributes.position.array[k + 0];
                var z = myBlock.geometry.attributes.position.array[k + 2];
                if (z > getGridElevation(n + WEBGLyTranslate, e + WEBGLxTranslate, grid))
                    above = true;
                else
                    below = true;
                if (above && below) break; // intersect surface
            }
            if (above) {
                if (below) {
                    var newBoxGeometry = tmpBox.clone();
                    newBoxGeometry.attributes.position.array = myBlock.geometry.attributes.position.array.slice(i, i + pointsPerCube);
                    for (var materialGroupIndex = 0, z = myBlock.geometry.groups.length; materialGroupIndex < z; materialGroupIndex++) {
                        var myGeometryGroup = myBlock.geometry.groups[materialGroupIndex];
                        if (i >= myGeometryGroup.start && i < myGeometryGroup.start + myGeometryGroup.count) {
                            var newMaterial = myBlock.material.materials[myGeometryGroup.materialIndex].clone();
                            var mesh = new THREE.Mesh(newBoxGeometry, newMaterial)
                            scene.add(mesh);
                            break;
                        }
                    }
                }
                for (var k = i; k < i + pointsPerCube; k++) {
                    myBlock.geometry.attributes.position.array[k] = undefined;
                }
            }
        }

        myBlock.geometry.attributes.position.needsUpdate = true;

    }

我得到了相当随机的结果。合并是如何设置位置数组的，是合并顶点还是只是追加？

Answer 1

从我的 cmets 中可以看出，tmpBox 之间的顶点数与合并的 blockModel 中每个框的顶点数不同。顶点的这种变化是因为原始合并是从 boxGeometry 进行的，合并，然后转换为缓冲区几何。这就是合并网格的转换方式。

finalGeometry = new THREE.BufferGeometry().fromGeometry(tmpGeometry);

我能够通过使用以下方法创建 tmpBox 来解决该问题：

var tmpBox = new THREE.BufferGeometry().fromGeometry(new THREE.BoxGeometry(blockModel.x_step, blockModel.y_step, 2));

看起来很奇怪

new THREE.BufferGeometry().fromGeometry(new THREE.BoxGeometry(blockModel.x_step, blockModel.y_step, 2)) != new THREE.BoxBufferGeometry(blockModel.x_step, blockModel.y_step, 2);

但是它们有不同数量的顶点。我认为一个是使用 4 个顶点的面，另一个是使用三个顶点的面。