如何在 OpenGL ES 中应用投影和相机视图？

如何解决如何在 OpenGL ES 中应用投影和相机视图？

我尝试根据官方文档 (https://developer.android.com/training/graphics/opengl/projection#kotlin) 应用投影和相机视图。不幸的是，我得到了一个空屏幕而不是正三角形。下面是我的 onSurfaceCreated 和 onDrawFrame 函数。我填充了一个不在 onSurfaceChanged 函数中的投影变换矩阵（如文档中所示），因为我从未在我的应用程序中调用过它（在这种情况下，结果是相同的）。

override fun onSurfaceCreated(unused: GL10,config: EGLConfig) {
   mTriangle = Triangle()
   GLES20.glClearColor(0.0f,0.0f,1.0f)
   Matrix.frustumM(projectionMatrix,-ratio,ratio,-1f,1f,3f,7f)
}

override fun onDrawFrame(unused: GL10) {
    GLES20.glClear(GLES20.GL_COLOR_BUFFER_BIT)

    // Set the camera position (View matrix)
    Matrix.setLookAtM(viewMatrix,0f,-3f,1.0f,0.0f)

    // Calculate the projection and view transformation
    Matrix.multiplyMM(vPMatrix,projectionMatrix,viewMatrix,0)

    // Draw shape
    mTriangle.draw(vPMatrix)
}

然后我想出了重写我的绘图功能。首先，我按照文档中的说明设置了 vertexshadercode。

private val 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;" +
                "}"

其次我改变了函数本身：

fun draw(mvpMatrix: FloatArray) { // pass in the calculated transformation matrix

    // get handle to shape's transformation matrix
    vPMatrixHandle = GLES20.glGetUniformlocation(program,"uMVPMatrix")

    // Pass the projection and view transformation to the shader
    GLES20.gluniformMatrix4fv(vPMatrixHandle,1,false,mvpMatrix,0)

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

   // disable vertex array
   GLES20.gldisabLevertexAttribArray(positionHandle)

}

我得到了一个空屏幕...然后我尝试将上面的代码和它的工作版本结合起来。我得到：

 fun draw(mvpMatrix: FloatArray) {
    // Add program to OpenGL ES environment
    GLES20.gluseProgram(mProgram)

    // get handle to vertex shader's vPosition member
    positionHandle = GLES20.glGetAttribLocation(mProgram,"vPosition").also {

        // Enable a handle to the triangle vertices
        GLES20.glEnabLevertexAttribArray(it)

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

        // get handle to fragment shader's vColor member
        mColorHandle = GLES20.glGetUniformlocation(mProgram,"vColor").also { colorHandle ->

            // Set color for drawing the triangle
            GLES20.gluniform4fv(colorHandle,color,0)
        }

        // get handle to shape's transformation matrix
        vPMatrixHandle = GLES20.glGetUniformlocation(mProgram,"uMVPMatrix")

        // Pass the projection and view transformation to the shader
        GLES20.gluniformMatrix4fv(vPMatrixHandle,0)

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

        // disable vertex array
        GLES20.gldisabLevertexAttribArray(it)
    }
}

这也不起作用。我怎样才能画出我的三角形？

附言

将 3f->2f->1f 更改为 Matrix.frustumM(projectionMatrix,7f) 处的“near”值没有任何作用
在具有第二个（大）版本 draw 函数的 gl_Position = vPosition; 中使用 gl_Position = uMVPMatrix * vPosition; 而不是 vertexshadercode 给出三角形。问题似乎出在矩阵上。

解决方法

好的，终于成功了！

使用了 Matrix.frustumM(projectionMatrix,-1.5f,1.5f,-1f,1f,7f)，也许一切都和上面一样。