我刚刚开始学习 OpenGL ES，但在理解顶点和索引的工作方式时遇到了一些麻烦。我目前的理解是，顶点是形状本身的一个点，索引代表顶点内的“三角形”。我正在按照一个教程来定义顶点和索引点，如下所示......
顶点数据
-1.0f, -1.0f 1.0f, -1.0f -1.0f, 1.0f 1.0f, 1.0f
指数数据
0,3,1, 0,2,3
我知道定义索引应该总是从一个顶点开始，但对我来说这些数字只是不加起来。当我在纸上画这个时，看起来实际绘制的图像应该是两个三角形在一起，形成一个“皇冠”形状。有人可以解释为什么这实际上是在画一个正方形而不是我期待的“皇冠”吗？
Square 类的源代码：
public class Square {
private FloatBuffer mFVertexBuffer;
private ByteBuffer mColorBuffer;
private ByteBuffer mIndexBuffer;
public Square() {
// 2D Points
float[] square = {
-1.0f, -1.0f,
1.0f, -1.0f,
-1.0f, 1.0f,
1.0f, 1.0f,
};
byte maxColor = (byte) 225;
/**
* Each line below represents RGB + Alpha transparency
*/
byte colors[] = {
0, maxColor, 0, maxColor,
0, maxColor, maxColor, maxColor,
0, 0, 0, maxColor,
maxColor, 0, maxColor, maxColor,
};
//triangles
byte[] indicies = {
0,3,1,
0,2,3
};
/**
* Make sure that bytes are in correct order, otherwise they might be
* drawn backwards
*/
ByteBuffer byteBuffer = ByteBuffer.allocateDirect(square.length * 4);
byteBuffer.order(ByteOrder.nativeOrder());
mFVertexBuffer = byteBuffer.order(ByteOrder.nativeOrder())
.asFloatBuffer();
mFVertexBuffer.put(square);
mFVertexBuffer.position(0);
mColorBuffer = ByteBuffer.allocateDirect(colors.length);
mColorBuffer.put(colors);
mColorBuffer.position(0);
mIndexBuffer = ByteBuffer.allocateDirect(indicies.length);
mIndexBuffer.put(indicies);
mIndexBuffer.position(0);
}
public void draw(GL10 gl) {
/**
* Make open GL only draw the front of the triangle (GL_CW = Graphics
* Library Clockwise)
*
* Back of triangle will not be drawn
*/
gl.glFrontFace(GL11.GL_CW);
/**
* specifies number of elements per vertex
*
* specifies floating point type
*
* Sets stride = 0 bytes* (Stride allows to use different types of data
* interchangably with opengl )
*/
gl.glVertexPointer(2, GL11.GL_FLOAT, 0, mFVertexBuffer);
// 4 because we are using 4 colors in our color bufer array
gl.glColorPointer(4, GL11.GL_UNSIGNED_BYTE, 0, mColorBuffer);
/**
* draws the image
*
* first argument specifies geomety format
*/
gl.glDrawElements(GL11.GL_TRIANGLES, 6, GL11.GL_UNSIGNED_BYTE,
mIndexBuffer);
// Reset to CounterClockwise
gl.glFrontFace(GL11.GL_CCW);
}
}
如果需要更多信息，请告诉我...