绘制基本三角形时的拼图效果

Question

我一直在关注 Android 在 https://developer.android.com/training/graphics/opengl 的培训 material，但是我已经阅读了指南并重新制作了两次，并且在这里和那里进行了更改但是不能'似乎看不出我做错了什么？在我看来，mTriangle 被创建了多次，或者它的数据在重绘之前没有被删除，在旋转时给它一个拼图效果。我的代码：

class GameRenderer : GLSurfaceView.Renderer {
    private lateinit var mTriangle: Triangle
    private val vPMatrix: FloatArray = FloatArray(16)
    private val projectionMatrix: FloatArray = FloatArray(16)
    private val viewMatrix: FloatArray = FloatArray(16)
    private val rotationMatrix: FloatArray = FloatArray(16)

    override fun onSurfaceCreated(unused: GL10, config: EGLConfig) {
        GLES20.glClearColor(0.0f, 0.0f, 0.0f, 1.0f)
        mTriangle = Triangle()
    }

    override fun onDrawFrame(unused: GL10) {
        GLES20.glClearColor(0.0f, 0.0f, 0.0f, 1.0f)
        val scratch = FloatArray(16)
        val time = SystemClock.uptimeMillis() % 4000L
        val angle = 0.090f * time.toInt()
        Matrix.setLookAtM(viewMatrix, 0, 0f, 0f, -3f, 0f, 0f, 0f, 0f, 1.0f, 0.0f)
        Matrix.multiplyMM(vPMatrix, 0, projectionMatrix, 0, viewMatrix, 0)
        Matrix.setRotateM(rotationMatrix, 0, angle, 0f, 0f, -1.0f)
        Matrix.multiplyMM(scratch, 0, vPMatrix, 0, rotationMatrix, 0)
        mTriangle.draw(scratch)
    }

    override fun onSurfaceChanged(unused: GL10, width: Int, height: Int) {
        GLES20.glViewport(0, 0, width, height)
        val ratio: Float = width.toFloat() / height.toFloat()
        Matrix.frustumM(projectionMatrix, 0, -ratio, ratio, -1f, 1f, 3f, 7f)
    }
}

这是渲染器的代码，三角形本身是：

class Triangle {
    private var mProgram: Int
    private val fragmentShaderCode: String =
        "precision mediump float;\n" +
        "uniform vec4 vColor;\n" +
        "void main() {\n" +
            "\tgl_FragColor = vColor;\n" +
        "}"
    private val vertexShaderCode: String =
        "uniform mat4 uMVPMatrix;\n" +
        "attribute vec4 vPosition;\n" +
        "void main() {\n" +
            "\tgl_Position = uMVPMatrix * vPosition;\n" +
        "}"

    private var vPMatrixHandle: Int = 0
    private var positionHandle: Int = 0
    private var mColorHandle: Int = 0

    private val COORDS_PER_VERTEX: Int = 3
    private var triangleCoords: FloatArray = floatArrayOf(     // 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 val color: FloatArray = floatArrayOf(0.63671875f, 0.76953125f, 0.22265625f, 1.0f)

    private val vertexCount: Int = triangleCoords.size / COORDS_PER_VERTEX
    private val vertexStride: Int = COORDS_PER_VERTEX * 4

    private var vertexBuffer: FloatBuffer =
        ByteBuffer.allocateDirect(triangleCoords.size * 4).run {
            order(ByteOrder.nativeOrder())
            asFloatBuffer().apply {
                put(triangleCoords)
                position(0)
            }
        }

    init {
        val vertexShader: Int = loadShader(GLES20.GL_VERTEX_SHADER, vertexShaderCode)
        val fragmentShader: Int = loadShader(GLES20.GL_FRAGMENT_SHADER, fragmentShaderCode)
        mProgram = GLES20.glCreateProgram().also {
            GLES20.glAttachShader(it, vertexShader)
            GLES20.glAttachShader(it, fragmentShader)
            GLES20.glLinkProgram(it)
        }
    }

    fun loadShader(type: Int, shaderCode: String): Int {
        return GLES20.glCreateShader(type).also { shader ->
            GLES20.glShaderSource(shader, shaderCode)
            GLES20.glCompileShader(shader)
        }
    }

    fun draw(mvpMatrix: FloatArray) {
        GLES20.glUseProgram(mProgram)
        positionHandle = GLES20.glGetAttribLocation(mProgram, "vPosition").also {
            GLES20.glEnableVertexAttribArray(it)
            GLES20.glVertexAttribPointer(
                it,
                COORDS_PER_VERTEX,
                GLES20.GL_FLOAT,
                false,
                vertexStride,
                vertexBuffer
            )
            mColorHandle = GLES20.glGetUniformLocation(mProgram, "vColor").also { colorHandle ->
                GLES20.glUniform4fv(colorHandle, 1, color, 0)
            }
            vPMatrixHandle = GLES20.glGetUniformLocation(mProgram, "uMVPMatrix")
            GLES20.glUniformMatrix4fv(vPMatrixHandle, 1, false, mvpMatrix, 0)
            GLES20.glDrawArrays(GLES20.GL_TRIANGLES, 0, vertexCount)
            GLES20.glDisableVertexAttribArray(it)
        }
    }
}

Answer 1

您没有清除帧缓冲区。注意 glClearColor specify clear values for the color buffers. But you've to invoke glClear 设置缓冲区的值：

GLES20.glClearColor(0.0f, 0.0f, 0.0f, 1.0f)
GLES20.glClear(GLES20.GL_COLOR_BUFFER_BIT)

绘制基本三角形时的拼图效果

Jigsaw Effect While Drawing Basic Triangle

android

kotlin

opengl-es

opengl-es-2.0