如何使renderscript汽缸 [英] How to make a cylinder in renderscript

问题描述

我一直在努力使renderscript一个圆柱体。这是code我尝试过：

I have been trying to make a cylinder in renderscript. This is the code I've tried:

public Mesh cylinder(){
    float radius=1.25f, halfLength=5;
    int slices=16;

    Mesh.TriangleMeshBuilder mbo= new TriangleMeshBuilder(mRSGL,3, Mesh.TriangleMeshBuilder.TEXTURE_0);
    for(int i=0; i<slices; i++) {
    float theta = (float) (((float)i)*2.0*Math.PI);
    float nextTheta = (float) (((float)i+1)*2.0*Math.PI);

        /*vertex at middle of end*/
    mbo.addVertex(0.0f, halfLength, 0.0f);

        /*vertices at edges of circle*/
    mbo.addVertex((float)(radius*Math.cos(theta)), halfLength, (float)(radius*Math.sin(theta)));
        mbo.addVertex((float)(radius*Math.cos(nextTheta)), halfLength, (float)(radius*Math.sin(nextTheta)));

        /* the same vertices at the bottom of the cylinder*/

    mbo.addVertex((float)(radius*Math.cos(nextTheta)), -halfLength, (float)(radius*Math.sin(nextTheta)));
    mbo.addVertex((float)(radius*Math.cos(theta)), halfLength, (float)(radius*Math.sin(theta)));
    mbo.addVertex(0.0f, -halfLength, 0.0f);

    mbo.addTriangle(0, 1, 2);
    mbo.addTriangle(3, 4, 5);


}
    return mbo.create(true);

}

但是，这code给我长5.任何我要去哪里错了思想的矩形？

But this code gives me a rectangle of length 5. Any ideas where I'm going wrong?

推荐答案

您确实有一些问题在这里。首先，你的角度始终等于二皮的倍数。您需要通过扇区数，当你计算你的角度来划分。另外在此步骤中，您有一个不必要的显式类型转换，java会处理整数转换为加倍给你。

You actually have a few problems here. First, your angles are always equal to multiples of 2pi. You need to divide by the number of sectors when you calculate your angles. Additionally in this step you have an unnecessary explicit type conversion, java will handle the conversion of integer to double for you.

其次，你会不断地添加相同的两个三角形网格和不加入任何三角形的圆筒的侧面，就在两个端面。在你的循环调用时addTriangle（），你应该使用索引，例如addTriangle（N，N + 1，N + 2）。

Second, you are constantly adding the same two triangles to the mesh and not adding any triangles for the side of the cylinder, just the two end faces. In your loop when calling addTriangle() you should use indices, for example addTriangle(n, n+1, n+2).

最后，你缺少一个负号，当你创建你的第4个顶点，所以它实际上是在halfLength，不-halfLength。

Finally, you were missing a negative sign when you created your 4th vertex, so it was actually at halfLength, not -halfLength.

试试这个：

public Mesh cylinder(){
    float radius=1.25f, halfLength=5;
    int slices=16;

    Mesh.TriangleMeshBuilder mbo= new TriangleMeshBuilder(mRSGL,3, Mesh.TriangleMeshBuilder.TEXTURE_0);

    /*vertex at middle of end*/
    mbo.addVertex(0.0f, halfLength, 0.0f);
    mbo.addVertex(0.0f, -halfLength, 0.0f);

    for(int i=0; i<slices; i++) {
         float theta = (float) (i*2.0*Math.PI / slices);
         float nextTheta = (float) ((i+1)*2.0*Math.PI / slices);

         /*vertices at edges of circle*/
         mbo.addVertex((float)(radius*Math.cos(theta)), halfLength, (float)(radius*Math.sin(theta)));
         mbo.addVertex((float)(radius*Math.cos(nextTheta)), halfLength, (float)(radius*Math.sin(nextTheta)));

         /* the same vertices at the bottom of the cylinder*/
         mbo.addVertex((float)(radius*Math.cos(nextTheta)), -halfLength, (float)(radius*Math.sin(nextTheta)));
         mbo.addVertex((float)(radius*Math.cos(theta)), -halfLength, (float)(radius*Math.sin(theta)));

         /*Add the faces for the ends, ordered for back face culling*/
         mbo.addTriangle(4*i+3, 4*i+2, 0); 
         //The offsets here are to adjust for the first two indices being the center points. The sector number (i) is multiplied by 4 because the way you are building this mesh, there are 4 vertices added with each sector
         mbo.addTriangle(4*i+5, 4*i+4, 1);
         /*Add the faces for the side*/
         mbo.addTriangle(4*i+2, 4*i+4, 4*i+5); 
         mbo.addTriangle(4*i+4, 4*i+2, 4*i+3);
    }
return mbo.create(true);

}

我也加入了其中创建只有一次的顶点为圆心轻微的优化，从而节省内存。索引的顺序这里是背面剔除。如果你想前面扭转它。如果您的需求，需要一个更有效的方法，最终，分配建设者允许使用trifans和tristrips，但对于这种复杂的网状便于三角形网格是值得。我有我自己的系统上运行此code，以确认它可以工作。

I have also added a slight optimization where the vertices for the centers of the circles are created only once, thus saving memory. The order of indices here is for back face culling. Reverse it if you want front face. Should your needs require a more efficient method eventually, allocation builders allow for using trifans and tristrips, but for a mesh of this complexity the ease of triangle meshes is merited. I have run this code on my own system to verify that it works.

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