处理（Java / Android）尝试使用for循环绘制形状

Question

I am trying to draw some triangles in 3D using Processing for Android. When I hard code the triangles (say, a sample of 10 triangles), they are drawn perfectly. However, when I try to draw those same triangles using a for loop, only one triangle is drawn. ( I am trying to draw 100 connected triangles, so hardcoding is not a really good solution)

Here is my for loop within the draw() function:

    for(int j=0;j<triangles.size();j++){
        beginShape(TRIANGLES);
    vertex(triangles.get(j)[0],triangles.get(j)[1],triangles.get(j)[2]); //triangle pt 1
    vertex(triangles.get(j)[3],triangles.get(j)[4],triangles.get(j)[5]); //triangle pt 2
    vertex(triangles.get(j)[6],triangles.get(j)[7],triangles.get(j)[8]); //triangle pt 3
    endShape(CLOSE);
    }

triangles is an ArrayList of float[9], where float[0-2] represents the x,y and z coordinates of the first point of the first triangle, float[3-5] represents the x,y and z coords of the second point of the first triangle and so on.

Visually it can be represented as:

ArrayList{
Triangle1.firstpoint.x(),Triangle1.firstpoint.y(),Triangle1.firstpoint.z(), Triangle1.secondpoint.x()...Triangle1.thirdpoint.x()...
Triangle2.firstpoint.x()...
and so on...
}

j represents the triangle number. (first tri, second tri etc)

When I try to hardcode 10 triangles, however, it works perfectly.

Hardcoding like this works perfectly:

    vertex((float) 12.0,(float)123.6016745697409,(float)13.154318796014476);
    vertex( (float)0.0,(float)197.68424385921847,(float)23.124972474732054);
    vertex((float) 20.0,(float)143.86712094263626,(float)44.91428537210794);

    vertex((float) 0.0,(float)197.68424385921847,(float)23.124972474732054);
    vertex( (float)24.0,(float)214.61268970017602,(float)45.76677898884916);
    vertex( (float)32.0,(float)188.10247423402564,(float)28.491849521501333);

    vertex((float) 56.0,(float)88.25218560204328,(float)12.036878675294194);
    vertex((float) 60.0,(float)144.49729617140488,(float)46.869886728176354);
    vertex((float) 76.0,(float)101.60603981125132,(float)7.27525015602069);

    vertex( (float)60.0,(float)144.49729617140488,(float)46.869886728176354);
    vertex( (float)64.0,(float)184.21835869332358,(float)3.9402252833719453);
    vertex( (float)76.0,(float)101.60603981125132,(float)7.27525015602069);

    vertex((float) 4.0,(float)268.3209514804444,(float)18.52950131584495);
    vertex( (float)52.0,(float)349.93516427695124,(float)8.772515956684678);
    vertex( (float)72.0,(float)338.2777711567361,(float)21.563995998820793);

Putting beginShape(TRIANGLES) and endShape() outside of the for loop has no effect. Really puzzled by what's going on here :/

Answer 1

Silly me! It turns out that every triangle in the triangles ArrayList had the same value, thus in effect producing only 1 triangle during the display!

The issue was because in transferring values over to the triangles ArrayList, I did:

            float[] trianglesi=new float[9];
        for (int tt=0; tt<ntri; tt++)
    {

        trianglesi[0]=(float) points[triangles[tt].p1].x;
        trianglesi[1]=(float) points[triangles[tt].p1].y;
        trianglesi[2]=(float) points[triangles[tt].p1].z;

        trianglesi[3]=(float) points[triangles[tt].p2].x;
        trianglesi[4]=(float) points[triangles[tt].p2].y;
        trianglesi[5]=(float) points[triangles[tt].p2].z;

        trianglesi[6]=(float) points[triangles[tt].p3].x;
        trianglesi[7]=(float) points[triangles[tt].p3].y;
        trianglesi[8]=(float) points[triangles[tt].p3].z;

        triangles2.add(trianglesi);
    }

(Here triangles2 refer to the triangles ArrayList, and trianglesi refer to a "unit" triangle.)

However, I had to initiate the trianglesi within the for loop!

Thanks laalto for leading me to relook at my triangles implementation, though.