Question

我知道NaN意味着不是一个数字，但我不明白我是如何得到错误的。我正在做的是引用我的形状对象的顶点的值，这些顶点来自我的形状类，并在我的渲染器类中使用它们。当我在logcat上打印出顶点的值时，我看到它返回前5个顶点，然后每个其他顶点都是NaN。如果你看看我的logcat显示，在调用matrix.multiplyMM（）之前，顶点（vertex1）打印得很好。但是在调用之后，顶点（shapeverts）开始变成NaN。

for (int i = 0; i < Shape.vertices.length; i += Shape.COORDS_PER_VERTEX) {//only checking one vertex
        Log.i("vertex1", String.valueOf(Shape.vertices[i] + ", " + Shape.vertices[i+1] + ", " + Shape.vertices[i+2] + ", " + Shape.vertices[i+3]));

        Matrix.multiplyMM(shapeVerts, 0, mvp, 0, Shape.vertices, 0);//vertices multiplied by model view projection matrix

        Log.i("shapevertBf", String.valueOf(shapeVerts[i] + ", " + shapeVerts[i+1] + ", " + shapeVerts[i+2] + ", " + shapeVerts[i+3]));

        shapeVerts[i] = shapeVerts[i] / shapeVerts[i + 3];    //clip.x divided by clip.w
        shapeVerts[i + 1] = shapeVerts[i + 1] / shapeVerts[i + 3];//clip.y divided by clip.w
        shapeVerts[i + 2] = shapeVerts[i + 2] / shapeVerts[i + 3];//clip.y divided by clip.w

        Log.i("shapevertAf", String.valueOf(shapeVerts[i] + ", " + shapeVerts[i+1] + ", " + shapeVerts[i+2] + ", " + shapeVerts[i+3]));

logcat的

  06-10 13:59:27.983  13121-13189/com.example.james.rollingsphere I/vertex1﹕ 0.0, 0.0, 9.0, 1.0
06-10 13:59:27.993  13121-13189/com.example.james.rollingsphere I/shapevertBf﹕ 0.0, 0.0, 19.5, 12.0
06-10 13:59:27.993  13121-13189/com.example.james.rollingsphere I/shapevertAf﹕ 0.0, 0.0, 1.625, 12.0
06-10 13:59:27.993  13121-13189/com.example.james.rollingsphere I/vertex1﹕ 0.0, 0.0, 9.0, 1.0
06-10 13:59:27.993  13121-13189/com.example.james.rollingsphere I/shapevertBf﹕ 0.0, 0.0, 19.5, 12.0
06-10 13:59:27.993  13121-13189/com.example.james.rollingsphere I/shapevertAf﹕ 0.0, 0.0, 1.625, 12.0
06-10 13:59:27.993  13121-13189/com.example.james.rollingsphere I/vertex1﹕ 0.0, 0.0, 9.0, 1.0
06-10 13:59:27.993  13121-13189/com.example.james.rollingsphere I/shapevertBf﹕ 0.0, 0.0, 19.5, 12.0
06-10 13:59:27.993  13121-13189/com.example.james.rollingsphere I/shapevertAf﹕ 0.0, 0.0, 1.625, 12.0
06-10 13:59:27.993  13121-13189/com.example.james.rollingsphere I/vertex1﹕ 0.0, 0.0, 9.0, 1.0
06-10 13:59:27.993  13121-13189/com.example.james.rollingsphere I/shapevertBf﹕ 0.0, 0.0, 19.5, 12.0
06-10 13:59:27.993  13121-13189/com.example.james.rollingsphere I/shapevertAf﹕ 0.0, 0.0, 1.625, 12.0
06-10 13:59:28.003  13121-13189/com.example.james.rollingsphere I/vertex1﹕ 0.0, 0.0, 9.0, 1.0
06-10 13:59:28.003  13121-13189/com.example.james.rollingsphere I/shapevertBf﹕ 0.0, 0.0, 0.0, 0.0
06-10 13:59:28.003  13121-13189/com.example.james.rollingsphere I/shapevertAf﹕ NaN, NaN, NaN, 0.0
06-10 13:59:28.003  13121-13189/com.example.james.rollingsphere I/vertex1﹕ 5.290067, 0.0, 7.281153, 1.0
06-10 13:59:28.003  13121-13189/com.example.james.rollingsphere I/shapevertBf﹕ 0.0, 0.0, 0.0, 0.0
06-10 13:59:28.003  13121-13189/com.example.james.rollingsphere I/shapevertAf﹕ NaN, NaN, NaN, 0.0
06-10 13:59:28.003  13121-13189/com.example.james.rollingsphere I/vertex1﹕ 1.634721, 5.031153, 7.281153, 1.0
06-10 13:59:28.003  13121-13189/com.example.james.rollingsphere I/shapevertBf﹕ 0.0, 0.0, 0.0, 0.0
06-10 13:59:28.003  13121-13189/com.example.james.rollingsphere I/shapevertAf﹕ NaN, NaN, NaN, 0.0
06-10 13:59:28.003  13121-13189/com.example.james.rollingsphere I/vertex1﹕ -4.279755, 3.109423, 7.281153, 1.0
06-10 13:59:28.013  13121-13189/com.example.james.rollingsphere I/shapevertBf﹕ 0.0, 0.0, 0.0, 0.0
06-10 13:59:28.013  13121-13189/com.example.james.rollingsphere I/shapevertAf﹕ NaN, NaN, NaN, 0.0

编辑我更新了代码和logcat。有趣的是，w组件在Matrix.multiply之后开始为12但随后变为0。

Answer 1

问题是在这种情况下使用Matrix.multiplyMM没有意义。 multiplyMM用于将两个矩阵相乘以得到矩阵乘积，而您想要做的是将矩阵（模型视图投影矩阵）乘以向量（Shape.vertices中未转换的顶点）得到一个向量（你在shapeVerts中转换的顶点）。

你只获得5个结果的原因是你将顶点数组视为4x4矩阵，而实际上它是一个顶点数组，每个顶点有3个元素。 4x4矩阵有16个元素，占用的空间与5 1/3顶点相同，因此您可以在达到未初始化数据并开始获取零（导致NaN）等之前读出5个（无效）值。 / p>

要解决此问题，请使用Matrix.multiplyMV将顶点坐标乘以模型视图投影矩阵，将偏移量传递给正确的顶点，如下所示：

Matrix.multiplyMV(shapeVerts, i, mvp, 0, Shape.vertices, i);

Answer 2

当在java中将双精度数除以0.0时，我们会得到结果为NaN。

您可以参考以下Java文档

http://docs.oracle.com/javase/7/docs/api/java/lang/Double.html#NaN

matrix.multiply返回Nan

2 个答案: