【Android开发学习13】Android OpenGL ES 3D空间与glDrawArrays

1.四棱锥: 由4个三角形构成。
   四方体: 由6个三角形构成。

难点:在构建3D空间的顶点坐标时，要让对象绕自身的轴旋转，必须让对象的中心坐标总是(0.0f,0.0f,0.0f),
     并且三角形都是按逆时针次序绘制的。

2.3D空间的绘制:
GL_APICALL void GL_APIENTRY glDrawArrays (GLenum mode, GLint first, GLsizei count);
参数说明：
mode，绘制方式，OpenGL2.0以后提供以下参数：GL_POINTS、GL_LINES、GL_LINE_LOOP、GL_LINE_STRIP、GL_TRIANGLES、GL_TRIANGLE_STRIP、GL_TRIANGLE_FAN。
first，从数组缓存中的哪一位开始绘制，一般为0。
count，数组中顶点的数量。

3.绘制顶点数组:
//绘制三角锥
for(int i=0; i<4; i++)
{
    gl.glDrawArrays(GL10.GL_TRIANGLE_STRIP, i*3, 3);
}

//绘制四方体

for(int i=0; i<6; i++)
{
    gl.glDrawArrays(GL10.GL_TRIANGLE_STRIP, i*4, 4);
}

[附]构建顶点数组:

int one = 0x10000;
// 四棱锥顶点数组:
private IntBuffer triggerBuffer = IntBuffer.wrap(new int[]{
	0,one,0,
	-one,-one,0,
	one,-one,one,
				
	0,one,0,
	one,-one,one,
	one,-one,-one,
				
	0,one,0,
	one,-one,-one,
	-one,-one,-one,
				
	0,one,0,
	-one,-one,-one,
	-one,-one,one		 
});
// 四方体顶点数组:
private IntBuffer quaterBuffer = IntBuffer.wrap(new int[]{
	one,one,-one,
	-one,one,-one,
	one,one,one,
	-one,one,one,
					
	one,-one,one,
	-one,-one,one,
	one,-one,-one,
	-one,-one,-one,
					
	one,one,one,
	-one,one,one,
	one,-one,one,
	-one,-one,one,
					
	one,-one,-one,
	-one,-one,-one,
	one,one,-one,
	-one,one,-one,
					
	-one,one,one,
	-one,one,-one,
	-one,-one,one,
	-one,-one,-one,
					
	one, one, -one,
	one, one, one,
	one, -one, -one,
	one, -one, one,
});