禁用顶点属性数组后 glDrawArrays() 如何工作？

Question

我已经开始学习 android 的 Opengl ES 2.0。我正在使用从以下站点获取的代码段： http://www.learnopengles.com/android-lesson-two-ambient-and-diffuse-lighting/ 这是一个有 4 个数字的亮点：

    private final float[] mLightPosInModelSpace = new float[] {0.0f, 0.0f, 0.0f, 1.0f};

这个灯点在模型 space 中。以下函数用于绘制禁用顶点属性数组的点。

private void drawLight()
{
    final int pointMVPMatrixHandle = GLES20.glGetUniformLocation(mPointProgramHandle, "u_MVPMatrix");
    final int pointPositionHandle = GLES20.glGetAttribLocation(mPointProgramHandle, "a_Position");

    // Pass in the position.
    GLES20.glVertexAttrib3f(pointPositionHandle, mLightPosInModelSpace[0], mLightPosInModelSpace[1], mLightPosInModelSpace[2]);

    // Since we are not using a buffer object, disable vertex arrays for this attribute.
    GLES20.glDisableVertexAttribArray(pointPositionHandle);  

    // Pass in the transformation matrix.
    Matrix.multiplyMM(mMVPMatrix, 0, mViewMatrix, 0, mLightModelMatrix, 0);
    Matrix.multiplyMM(mMVPMatrix, 0, mProjectionMatrix, 0, mMVPMatrix, 0);
    GLES20.glUniformMatrix4fv(pointMVPMatrixHandle, 1, false, mMVPMatrix, 0);


    // Draw the point.
    GLES20.glDrawArrays(GLES20.GL_POINTS, 0, 1);
}

我从这里阅读了文档：https://www.khronos.org/opengles/sdk/docs/man/xhtml/glEnableVertexAttribArray.xml
并看到在启用顶点属性数组 glDrawArrays() 后从该启用的数组中获取点。但我的问题是 glDrawArrays() 从哪里得到积分？在此示例中，从 mLightPosInModelSpace 中获取观点可以正常工作。提前致谢。

Answer 1

参见 OpenGL ES 2.0 规范的第 2.7 节，“当前顶点状态”：

Current generic attribute values define generic attributes for a vertex when a vertex array defining that data is not enabled, as described in section 2.8.

A current value may be changed at any time by issuing one of the commands

void VertexAttrib{1234}{f}( uint index, T values );

void VertexAttrib{1234}{f}v( uint index, T values );

to load the given value(s) into the current generic attribute for slot index, whose components are named x, y, z, and w.

然后在第 21 页，规范解释了它们是如何被拉动的：

If an array corresponding to a generic attribute required by a vertex shader is not enabled, then the corresponding element is taken from the current generic attribute state (see section 2.7).

禁用顶点属性数组后 glDrawArrays() 如何工作？

After disabling Vertex Attribute Array how glDrawArrays() works?

android

opengl-es-2.0