Question

OpenGL / ArCore全新，存在一些问题。我想简单地在锚点附近绘制一个三角形，但无法弄清楚如何做到这一点。同时我还想绘制一条我有原点的线。方向向量。

我使用谷歌的ARCore示例项目作为基础。我可以使用他们的OpenGL教程在这个屏幕上绘制一个2D Triangle，其中包含以下Triangle类：

private final String vertexShaderCode =
        // This matrix member variable provides a hook to manipulate
        // the coordinates of the objects that use this vertex shader
        "uniform mat4 uMVPMatrix;" +
        "attribute vec4 vPosition;" +
        "void main() {" +
        // the matrix must be included as a modifier of gl_Position
        // Note that the uMVPMatrix factor *must be first* in order
        // for the matrix multiplication product to be correct.
        "  gl_Position = uMVPMatrix * vPosition;" +
        "}";

private final String fragmentShaderCode =
        "precision mediump float;" +
        "uniform vec4 vColor;" +
        "void main() {" +
        "  gl_FragColor = vColor;" +
        "}";

private final FloatBuffer vertexBuffer;
private final int mProgram;
private int mPositionHandle;
private int mColorHandle;
private int mMVPMatrixHandle;

// number of coordinates per vertex in this array
static final int COORDS_PER_VERTEX = 3;
static float triangleCoords[] = {
        // in counterclockwise order:
        0.0f,  0.622008459f, 0.0f,   // top
       -0.5f, -0.311004243f, 0.0f,   // bottom left
        0.5f, -0.311004243f, 0.0f    // bottom right
};
private final int vertexCount = triangleCoords.length / COORDS_PER_VERTEX;
private final int vertexStride = COORDS_PER_VERTEX * 4; // 4 bytes per vertex

float color[] = { 0.63671875f, 0.76953125f, 0.22265625f, 0.0f };

/**
 * Sets up the drawing object data for use in an OpenGL ES context.
 */
public Triangle() {
    // initialize vertex byte buffer for shape coordinates
    ByteBuffer bb = ByteBuffer.allocateDirect(
            // (number of coordinate values * 4 bytes per float)
            triangleCoords.length * 4);
    // use the device hardware's native byte order
    bb.order(ByteOrder.nativeOrder());

    // create a floating point buffer from the ByteBuffer
    vertexBuffer = bb.asFloatBuffer();
    // add the coordinates to the FloatBuffer
    vertexBuffer.put(triangleCoords);
    // set the buffer to read the first coordinate
    vertexBuffer.position(0);

    // prepare shaders and OpenGL program
    int vertexShader = MyGLRenderer.loadShader(
            GLES20.GL_VERTEX_SHADER, vertexShaderCode);
    int fragmentShader = MyGLRenderer.loadShader(
            GLES20.GL_FRAGMENT_SHADER, fragmentShaderCode);

    mProgram = GLES20.glCreateProgram();             // create empty OpenGL Program
    GLES20.glAttachShader(mProgram, vertexShader);   // add the vertex shader to program
    GLES20.glAttachShader(mProgram, fragmentShader); // add the fragment shader to program
    GLES20.glLinkProgram(mProgram);                  // create OpenGL program executables

}

/**
 * Encapsulates the OpenGL ES instructions for drawing this shape.
 *
 * @param mvpMatrix - The Model View Project matrix in which to draw
 * this shape.
 */
public void draw(float[] mvpMatrix) {
    // Add program to OpenGL environment
    GLES20.glUseProgram(mProgram);

    // get handle to vertex shader's vPosition member
    mPositionHandle = GLES20.glGetAttribLocation(mProgram, "vPosition");

    // Enable a handle to the triangle vertices
    GLES20.glEnableVertexAttribArray(mPositionHandle);

    // Prepare the triangle coordinate data
    GLES20.glVertexAttribPointer(
            mPositionHandle, COORDS_PER_VERTEX,
            GLES20.GL_FLOAT, false,
            vertexStride, vertexBuffer);

    // get handle to fragment shader's vColor member
    mColorHandle = GLES20.glGetUniformLocation(mProgram, "vColor");

    // Set color for drawing the triangle
    GLES20.glUniform4fv(mColorHandle, 1, color, 0);

    // get handle to shape's transformation matrix
    mMVPMatrixHandle = GLES20.glGetUniformLocation(mProgram, "uMVPMatrix");
    MyGLRenderer.checkGlError("glGetUniformLocation");

    // Apply the projection and view transformation
    GLES20.glUniformMatrix4fv(mMVPMatrixHandle, 1, false, mvpMatrix, 0);
    MyGLRenderer.checkGlError("glUniformMatrix4fv");

    // Draw the triangle
    GLES20.glDrawArrays(GLES20.GL_TRIANGLES, 0, vertexCount);

    // Disable vertex array
    GLES20.glDisableVertexAttribArray(mPositionHandle);
}

更改trianglecoords变量中的z值并不会影响绘制三角形，因此我对如何继续进行了混淆。

如果你需要知道原因，我试图做一些射线三角交叉测试;它运作得不好，想用一个三角形来测试它是如何工作的。我突然意识到这一点，让我感到非常恼火，看起来很复杂。

提前致谢！

修改的我知道GL很难进入ARCore。我的任务涉及到使用ARCore，但由于我也使用GL作为个人项目，我真的想了解它，而不是使用Unity / Unreal。

Answer 1

您可以通过设置正确的参数来用ShapeFactory.makeCylinder模仿一行。但是，这不是在OpenGL中，但肯定会为简单的行减少开销。

我的方法是获取两个行尾的起始词和结束词coodrinate点。然后计算直线的方向和距离，使用该距离作为圆柱体的长度。将线放在距离的中间，然后相应地旋转以适合实际的起点和终点。

在使用java的ARCore中，如何在我的世界中绘制3D三角形/线条

1 个答案: