Question

我正在使用opengl（GLES20）开发一个Android应用程序。我成功地渲染了正方形多边形模型但是我不能让他们看着相机。

我阅读了下面的帖子，但我没抓住重点。

Orientating Figures to look at the Camera with OpenGL

view.SampleGLSurfaceViewRenderer.kt

class SampleGLSurfaceViewRenderer() : GLSurfaceView.Renderer {
    var vertexShader: Int = -1
    var fragmentShader: Int = -1
    var shaderProgram: Int = -1

    var attributeHandlers: MutableMap<String, Int> = mutableMapOf()
    var uniformHandlers: MutableMap<String, Int> = mutableMapOf()

    var sampleData: SampleGLData = SampleGLData()

    var modelMatrix: FloatArray = FloatArray(16)
    var viewMatrix: FloatArray = FloatArray(16)
    var perspectiveMatrix: FloatArray = FloatArray(16)

    var aspect: Float = 0.0f

    override fun onSurfaceCreated(gl: GL10?, config: EGLConfig?) {
        GLES20.glClearColor(0.0f, 0.0f, 0.0f, 1.0f)

        initShadersAndProgram()

        initLocationHandlers()
    }

    override fun onSurfaceChanged(gl: GL10?, width: Int, height: Int) {
        GLES20.glViewport(0, 0, width, height)

        aspect = width * 1.0f / height
    }

    override fun onDrawFrame(gl: GL10?) {
        GLES20.glClear(GLES20.GL_COLOR_BUFFER_BIT or GLES20.GL_DEPTH_BUFFER_BIT)
        GLES20.glEnable(GLES20.GL_DEPTH_TEST)

        GLES20.glUseProgram(shaderProgram)

        attributeHandlers["position"]?.also { positionHandle ->
            GLES20.glEnableVertexAttribArray(positionHandle)

            GLES20.glVertexAttribPointer(positionHandle, 3, GLES20.GL_FLOAT, false, 12, sampleData.vertexBuffer)

            resetMvpMatrix()
            applyMvpMatrix()

            GLES20.glDrawElements(GLES20.GL_TRIANGLES, sampleData.indicesBuffer.capacity(), GLES20.GL_UNSIGNED_SHORT, sampleData.indicesBuffer)

            resetMvpMatrix()
            Matrix.translateM(modelMatrix, 0, 0.0f, -4.0f, 0.0f)
            applyMvpMatrix()

            GLES20.glDrawElements(GLES20.GL_TRIANGLES, sampleData.indicesBuffer.capacity(), GLES20.GL_UNSIGNED_SHORT, sampleData.indicesBuffer)

            GLES20.glDisableVertexAttribArray(positionHandle)
        }
    }

    private fun applyMvpMatrix() {
        uniformHandlers["mvpMatrix"]?.also { mvpMatrixHandler ->
            val mvpMatrix: FloatArray = FloatArray(16)
            Matrix.multiplyMM(mvpMatrix, 0, perspectiveMatrix, 0, viewMatrix, 0)
            Matrix.multiplyMM(mvpMatrix, 0, mvpMatrix, 0, modelMatrix, 0)

            GLES20.glUniformMatrix4fv(mvpMatrixHandler, 1, false, mvpMatrix, 0)
        }
    }

    private fun resetMvpMatrix() {
        Matrix.setIdentityM(modelMatrix, 0)

        Matrix.setLookAtM(viewMatrix, 0,
                0.0f, 0.4f, -1.0f,
                0.0f, 0.0f, 0.0f,
                0.0f, 1.0f, 0.0f)

        Matrix.perspectiveM(perspectiveMatrix, 0,
                120.0f,
                aspect,
                0.1f, 10.0f)
    }

    private fun initLocationHandlers() {
        attributeHandlers.put("position", GLES20.glGetAttribLocation(shaderProgram, "position"))

        uniformHandlers.put("mvpMatrix", GLES20.glGetUniformLocation(shaderProgram, "mvpMatrix"))
    }

    private fun initShadersAndProgram() {
        val vertexShaderSource = """
            attribute vec3 position;
            uniform mat4 mvpMatrix;
            void main(void) {
                gl_Position = mvpMatrix * vec4(position, 1.0);
            }
        """.trimIndent()

        val fragmentShaderSource = """
            precision mediump float;
            void main(void) {
                gl_FragColor = vec4(1.0, 1.0, 1.0, 1.0);
            }
        """.trimIndent()

        vertexShader = GLES20.glCreateShader(GLES20.GL_VERTEX_SHADER)
        GLES20.glShaderSource(vertexShader, vertexShaderSource)
        GLES20.glCompileShader(vertexShader)

        fragmentShader = GLES20.glCreateShader(GLES20.GL_FRAGMENT_SHADER)
        GLES20.glShaderSource(fragmentShader, fragmentShaderSource)
        GLES20.glCompileShader(fragmentShader)

        shaderProgram = GLES20.glCreateProgram()
        GLES20.glAttachShader(shaderProgram, vertexShader)
        GLES20.glAttachShader(shaderProgram, fragmentShader)
        GLES20.glLinkProgram(shaderProgram)
    }
}

data.SampleGLData.kt

class SampleGLData {
    var vertexCoords: Int = 4
    val vertexArray: FloatArray
    val vertexBuffer: FloatBuffer
    val indicesArray: ShortArray
    val indicesBuffer: ShortBuffer

    init {
        vertexArray = floatArrayOf(
                -1.0f, 1.0f, 1.0f,
                -1.0f, -1.0f, 1.0f,
                1.0f, -1.0f, 1.0f,
                1.0f, 1.0f, 1.0f
        )

        vertexBuffer = createFloatBuffer(vertexArray)

        indicesArray = shortArrayOf(
                0, 1, 2,
                0, 2, 3
        )

        indicesBuffer = createShortBuffer(indicesArray)
    }

    fun createFloatBuffer(array: FloatArray): FloatBuffer {
        return ByteBuffer.allocateDirect(array.size * 4).run {
            order(ByteOrder.nativeOrder())
            asFloatBuffer().apply {
                put(array)
                position(0)
            }
        }
    }

    fun createShortBuffer(array: ShortArray): ShortBuffer {
        return ByteBuffer.allocateDirect(array.size * 2).run {
            order(ByteOrder.nativeOrder())
            asShortBuffer().apply {
                put(array)
                position(0)
            }
        }
    }
}

当前，多边形与XY曲面平行渲染。我想使其旋转成与摄影机的视线垂直。

我画了我想做什么。像“最佳”部分一样，我希望所有多边形都看着相机。谢谢。

Answer 1

当前，多边形与XY曲面平行渲染。我想使其旋转成与摄影机的视线垂直。

您必须向模型添加一个billboard矩阵，该矩阵在视图矩阵上的方向为inverse。这会将模型定向为与视口平行：

Matrix.invertM(billboard, 0, viewMatrix, 0)
billboard[12] = 0.0f
billboard[13] = 0.0f
billboard[14] = 0.0f

如果要使其垂直于视口，则必须绕X轴额外旋转90度。

Matrix.setIdentityM(rotateX, 0)
Matrix.rotateM(rotateX, 0, 90.0f, 1.0f, 0.0f, 0.0f)

将此转换应用于模型视图矩阵，如下所示：

private fun applyMvpMatrix() {

    uniformHandlers["mvpMatrix"]?.also { mvpMatrixHandler ->

        val rotateX: FloatArray = FloatArray(16)
        val billboard: FloatArray = FloatArray(16)
        val mvpMatrix: FloatArray = FloatArray(16)

        Matrix.setIdentityM(rotateX, 0)
        Matrix.rotateM(rotateX, 0, 90.0f, 1.0f, 0.0f, 0.0f)

        Matrix.invertM(billboard, 0, viewMatrix, 0)
        billboard[12] = 0.0f
        billboard[13] = 0.0f
        billboard[14] = 0.0f

        Matrix.multiplyMM(mvpMatrix, 0, perspectiveMatrix, 0, viewMatrix, 0)
        Matrix.multiplyMM(mvpMatrix, 0, mvpMatrix, 0, modelMatrix, 0)
        Matrix.multiplyMM(mvpMatrix, 0, mvpMatrix, 0, rotateX, 0)
        Matrix.multiplyMM(mvpMatrix, 0, mvpMatrix, 0, billboard, 0)

        GLES20.glUniformMatrix4fv(mvpMatrixHandler, 1, false, mvpMatrix, 0)
    }
}

如果您希望模型始终面对modelMatrix定义的平移镜头，则必须更改应用modelMatrix和{{1}的方式}矩阵。由于模型应与视口平行，因此在这种情况下，旋转90度（billboard）的旋转是无用的：

rotateX

如何使多边形看着相机（OpenGL）？

1 个答案: