Hello EGL

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Hello EGL

作者: 功夫羊 kongfu.yang(a)gmail.com

日期: 2010-01-28

本文介绍第一个 OpenGL ES程序：Hello EGL

注：本文中例子针对Windows CE平台编写。

OpenGL ES简化了模型描述，取消了通过在 glBegin/glEnd 之间使用大量glVertex之类的调用来逐点描述模型，统一到使用VertexArray。

下面我们就来画一个简单的物体：用三角形拼出的HELLO EGL。该物体的示意图如下：

图：helloegl certex layout

照例，先New App：

图：new app

然后设置一下项目属性：

图：project properties

共有三处要改的，使得该项目可以利用上如下图所示的库和头文件：

图：my lib files

首先是头文件包含目录：

图：project include dir

然后是库文件目录：

图：project lib dir

最后是OpenGL ES库：

图：project egl lib

OK，环境准备好了，可以写代码了。先把我们准备好的OpenGL ES初始化代码加上：

图：code skeleton

最后标记出来的那个draw()函数就是实际绘制HELLO EGL的代码了：

图 draw code

正如前面提过的，我们只能通过 VERTEX_ARRAY 批量的将模型顶点坐标发送给 OpenGL ES，为此需要先 glEnableClientState() 以打开相关支持。为了让世界看上去更美好一点，我还用 ColorArray 给每个顶点指定了颜色。然后通过 glVertexPointer/glColorPointer 将数据发送出去，再通过 glDrawArrays(GL_TRIANGLES) 进行绘制。值得一提的是，目前 GLES 不支持 GL_QUADS。除了调用 glDrawArrays()，OpenGL ES 还提供了更为灵活的 glDrawElements() 方法，值得看一下规范里的说明。


glEnableClientState (GL_VERTEX_ARRAY);
glEnableClientState (GL_NORMAL_ARRAY);
glEnableClientState (GL_TEXTURE_COORD_ARRAY);
glEnableClientState (GL_COLOR_ARRAY);

glVertexPointer (...);
glColorPointer (...);

glDrawArrays (GL_TRIANGLES);
glDrawElements ();

剩下的奥密就全在数组 helloVertex 里了。其实它的内容已经完全表示的本文开始的那张示意图里了，建议您自己推算一下，以熟悉 TRIANGLES 建模。这个小小的例子也可以利用 GL_TRIANG_STRIP 得到很大的优化，感兴趣的可以练习一下。

代码如下：hellomesh.h


#ifndef _HELLO_MESH_
#define _HELLO_MESH_

GLfixed helloVertex[] = {	// HELLO EGL
	// H
	Float2Fixed(0.0f), Float2Fixed(0.0f),  Float2Fixed(0.1f), Float2Fixed(0.0f),  Float2Fixed(0.1f), Float2Fixed(0.7f),
	Float2Fixed(0.0f), Float2Fixed(0.0f),  Float2Fixed(0.1f), Float2Fixed(0.7f),  Float2Fixed(0.0f), Float2Fixed(0.7f),

	Float2Fixed(0.1f), Float2Fixed(0.3f),  Float2Fixed(0.3f), Float2Fixed(0.3f),  Float2Fixed(0.3f), Float2Fixed(0.4f),
	Float2Fixed(0.1f), Float2Fixed(0.3f),  Float2Fixed(0.3f), Float2Fixed(0.4f),  Float2Fixed(0.1f), Float2Fixed(0.4f),

	Float2Fixed(0.3f), Float2Fixed(0.0f),  Float2Fixed(0.4f), Float2Fixed(0.0f),  Float2Fixed(0.4f), Float2Fixed(0.7f),
	Float2Fixed(0.3f), Float2Fixed(0.0f),  Float2Fixed(0.4f), Float2Fixed(0.7f),  Float2Fixed(0.3f), Float2Fixed(0.7f),

	// E
	Float2Fixed(0.5f), Float2Fixed(0.0f),  Float2Fixed(0.6f), Float2Fixed(0.0f),  Float2Fixed(0.6f), Float2Fixed(0.7f),
	Float2Fixed(0.5f), Float2Fixed(0.0f),  Float2Fixed(0.6f), Float2Fixed(0.7f),  Float2Fixed(0.5f), Float2Fixed(0.7f),

	Float2Fixed(0.6f), Float2Fixed(0.0f),  Float2Fixed(0.9f), Float2Fixed(0.0f),  Float2Fixed(0.9f), Float2Fixed(0.1f),
	Float2Fixed(0.6f), Float2Fixed(0.0f),  Float2Fixed(0.9f), Float2Fixed(0.1f),  Float2Fixed(0.6f), Float2Fixed(0.1f),

	Float2Fixed(0.6f), Float2Fixed(0.3f),  Float2Fixed(0.9f), Float2Fixed(0.3f),  Float2Fixed(0.9f), Float2Fixed(0.4f),
	Float2Fixed(0.6f), Float2Fixed(0.3f),  Float2Fixed(0.9f), Float2Fixed(0.4f),  Float2Fixed(0.6f), Float2Fixed(0.4f),

	Float2Fixed(0.6f), Float2Fixed(0.6f),  Float2Fixed(0.9f), Float2Fixed(0.6f),  Float2Fixed(0.9f), Float2Fixed(0.7f),
	Float2Fixed(0.6f), Float2Fixed(0.6f),  Float2Fixed(0.9f), Float2Fixed(0.7f),  Float2Fixed(0.6f), Float2Fixed(0.7f),

	// L
	Float2Fixed(1.0f), Float2Fixed(0.0f),  Float2Fixed(1.1f), Float2Fixed(0.0f),  Float2Fixed(1.1f), Float2Fixed(0.7f),
	Float2Fixed(1.0f), Float2Fixed(0.0f),  Float2Fixed(1.1f), Float2Fixed(0.7f),  Float2Fixed(1.0f), Float2Fixed(0.7f),

	Float2Fixed(1.1f), Float2Fixed(0.0f),  Float2Fixed(1.4f), Float2Fixed(0.0f),  Float2Fixed(1.4f), Float2Fixed(0.1f),
	Float2Fixed(1.1f), Float2Fixed(0.0f),  Float2Fixed(1.4f), Float2Fixed(0.1f),  Float2Fixed(1.1f), Float2Fixed(0.1f),

	// L
	Float2Fixed(1.5f), Float2Fixed(0.0f),  Float2Fixed(1.6f), Float2Fixed(0.0f),  Float2Fixed(1.6f), Float2Fixed(0.7f),
	Float2Fixed(1.5f), Float2Fixed(0.0f),  Float2Fixed(1.6f), Float2Fixed(0.7f),  Float2Fixed(1.5f), Float2Fixed(0.7f),

	Float2Fixed(1.6f), Float2Fixed(0.0f),  Float2Fixed(1.9f), Float2Fixed(0.0f),  Float2Fixed(1.9f), Float2Fixed(0.1f),
	Float2Fixed(1.6f), Float2Fixed(0.0f),  Float2Fixed(1.9f), Float2Fixed(0.1f),  Float2Fixed(1.6f), Float2Fixed(0.1f),

	// O
	Float2Fixed(2.0f), Float2Fixed(0.0f),  Float2Fixed(2.1f), Float2Fixed(0.0f),  Float2Fixed(2.1f), Float2Fixed(0.7f),
	Float2Fixed(2.0f), Float2Fixed(0.0f),  Float2Fixed(2.1f), Float2Fixed(0.7f),  Float2Fixed(2.0f), Float2Fixed(0.7f),

	Float2Fixed(2.1f), Float2Fixed(0.0f),  Float2Fixed(2.3f), Float2Fixed(0.0f),  Float2Fixed(2.3f), Float2Fixed(0.1f),
	Float2Fixed(2.1f), Float2Fixed(0.0f),  Float2Fixed(2.3f), Float2Fixed(0.1f),  Float2Fixed(2.1f), Float2Fixed(0.1f),

	Float2Fixed(2.1f), Float2Fixed(0.6f),  Float2Fixed(2.3f), Float2Fixed(0.6f),  Float2Fixed(2.3f), Float2Fixed(0.7f),
	Float2Fixed(2.1f), Float2Fixed(0.6f),  Float2Fixed(2.3f), Float2Fixed(0.7f),  Float2Fixed(2.1f), Float2Fixed(0.7f),

	Float2Fixed(2.3f), Float2Fixed(0.0f),  Float2Fixed(2.4f), Float2Fixed(0.0f),  Float2Fixed(2.4f), Float2Fixed(0.7f),
	Float2Fixed(2.3f), Float2Fixed(0.0f),  Float2Fixed(2.4f), Float2Fixed(0.7f),  Float2Fixed(2.3f), Float2Fixed(0.7f),

	// E
	Float2Fixed(2.5f), Float2Fixed(0.0f),  Float2Fixed(2.6f), Float2Fixed(0.0f),  Float2Fixed(2.6f), Float2Fixed(0.7f),
	Float2Fixed(2.5f), Float2Fixed(0.0f),  Float2Fixed(2.6f), Float2Fixed(0.7f),  Float2Fixed(2.5f), Float2Fixed(0.7f),

	Float2Fixed(2.6f), Float2Fixed(0.0f),  Float2Fixed(2.9f), Float2Fixed(0.0f),  Float2Fixed(2.9f), Float2Fixed(0.1f),
	Float2Fixed(2.6f), Float2Fixed(0.0f),  Float2Fixed(2.9f), Float2Fixed(0.1f),  Float2Fixed(2.6f), Float2Fixed(0.1f),

	Float2Fixed(2.6f), Float2Fixed(0.3f),  Float2Fixed(2.9f), Float2Fixed(0.3f),  Float2Fixed(2.9f), Float2Fixed(0.4f),
	Float2Fixed(2.6f), Float2Fixed(0.3f),  Float2Fixed(2.9f), Float2Fixed(0.4f),  Float2Fixed(2.6f), Float2Fixed(0.4f),

	Float2Fixed(2.6f), Float2Fixed(0.6f),  Float2Fixed(2.9f), Float2Fixed(0.6f),  Float2Fixed(2.9f), Float2Fixed(0.7f),
	Float2Fixed(2.6f), Float2Fixed(0.6f),  Float2Fixed(2.9f), Float2Fixed(0.7f),  Float2Fixed(2.6f), Float2Fixed(0.7f),

	// G
	Float2Fixed(3.1f), Float2Fixed(0.6f),  Float2Fixed(3.4f), Float2Fixed(0.6f),  Float2Fixed(3.4f), Float2Fixed(0.7f),
	Float2Fixed(3.1f), Float2Fixed(0.6f),  Float2Fixed(3.4f), Float2Fixed(0.7f),  Float2Fixed(3.1f), Float2Fixed(0.7f),

	Float2Fixed(3.0f), Float2Fixed(0.0f),  Float2Fixed(3.1f), Float2Fixed(0.0f),  Float2Fixed(3.1f), Float2Fixed(0.7f),
	Float2Fixed(3.0f), Float2Fixed(0.0f),  Float2Fixed(3.1f), Float2Fixed(0.7f),  Float2Fixed(3.0f), Float2Fixed(0.7f),

	Float2Fixed(3.1f), Float2Fixed(0.0f),  Float2Fixed(3.4f), Float2Fixed(0.0f),  Float2Fixed(3.4f), Float2Fixed(0.1f),
	Float2Fixed(3.1f), Float2Fixed(0.0f),  Float2Fixed(3.4f), Float2Fixed(0.1f),  Float2Fixed(3.1f), Float2Fixed(0.1f),

	Float2Fixed(3.3f), Float2Fixed(0.1f),  Float2Fixed(3.4f), Float2Fixed(0.1f),  Float2Fixed(3.4f), Float2Fixed(0.3f),
	Float2Fixed(3.3f), Float2Fixed(0.1f),  Float2Fixed(3.4f), Float2Fixed(0.3f),  Float2Fixed(3.3f), Float2Fixed(0.3f),

	Float2Fixed(3.25f), Float2Fixed(0.3f),  Float2Fixed(3.45f), Float2Fixed(0.3f),  Float2Fixed(3.45f), Float2Fixed(0.4f),
	Float2Fixed(3.25f), Float2Fixed(0.3f),  Float2Fixed(3.45f), Float2Fixed(0.4f),  Float2Fixed(3.25f), Float2Fixed(0.4f),

	// L
	Float2Fixed(3.5f), Float2Fixed(0.0f),  Float2Fixed(3.6f), Float2Fixed(0.0f),  Float2Fixed(3.6f), Float2Fixed(0.7f),
	Float2Fixed(3.5f), Float2Fixed(0.0f),  Float2Fixed(3.6f), Float2Fixed(0.7f),  Float2Fixed(3.5f), Float2Fixed(0.7f),

	Float2Fixed(3.6f), Float2Fixed(0.0f),  Float2Fixed(3.9f), Float2Fixed(0.0f),  Float2Fixed(3.9f), Float2Fixed(0.1f),
	Float2Fixed(3.6f), Float2Fixed(0.0f),  Float2Fixed(3.9f), Float2Fixed(0.1f),  Float2Fixed(3.6f), Float2Fixed(0.1f)
};

#define RED   Float2Fixed(1.0f) , Float2Fixed(0.0f) , Float2Fixed(0.0f) , Float2Fixed(1.0f)
#define GREEN Float2Fixed(0.0f) , Float2Fixed(1.0f) , Float2Fixed(0.0f) , Float2Fixed(1.0f)
#define BLUE  Float2Fixed(0.0f) , Float2Fixed(0.0f) , Float2Fixed(1.0f) , Float2Fixed(1.0f)

float helloColor[] = {	// HELLO EGL
	// H
	// 0.0,0.0, 0.1,0.0, 0.1,0.7,
	RED,          GREEN,       BLUE,
	// 0.0,0.0, 0.1,0.7, 0.0,0.7,
	RED,          GREEN,       BLUE,

	// 0.1,0.3, 0.3,0.3, 0.3,0.4,
	RED,          GREEN,       BLUE,
	// 0.1,0.3, 0.3,0.4, 0.1,0.4,
	RED,          GREEN,       BLUE,

	// 0.3,0.0, 0.4,0.0, 0.4,0.7,
	RED,          GREEN,       BLUE,
    // 0.3,0.0, 0.4,0.7, 0.3,0.7,
	RED,          GREEN,       BLUE,

	// E
	//0.5,0.0, 0.6,0.0, 0.6,0.7,
	RED,          GREEN,       BLUE,
	//0.5,0.0, 0.6,0.7, 0.5,0.7,
	RED,          GREEN,       BLUE,

	//0.6,0.0, 0.9,0.0, 0.9,0.1,
	RED,          GREEN,       BLUE,
	//0.6,0.0, 0.9,0.1, 0.6,0.1,
	RED,          GREEN,       BLUE,

	//0.6,0.3, 0.9,0.3, 0.9,0.4,
	RED,          GREEN,       BLUE,
	//0.6,0.3, 0.9,0.4, 0.6,0.4,
	RED,          GREEN,       BLUE,

	//0.6,0.6, 0.9,0.6, 0.9,0.7,
	RED,          GREEN,       BLUE,
	//0.6,0.6, 0.9,0.7, 0.6,0.7,
	RED,          GREEN,       BLUE,

	// L
	//1.0,0.0, 1.1,0.0, 1.1,0.7,
	RED,          GREEN,       BLUE,
	//1.0,0.0, 1.1,0.7, 1.0,0.7,
	RED,          GREEN,       BLUE,

	RED,          GREEN,       BLUE,
	//1.1,0.0, 1.4,0.0, 1.4,0.1,
	RED,          GREEN,       BLUE,
	//1.1,0.0, 1.4,0.1, 1.1,0.1,

	// L
	//1.5,0.0, 1.6,0.0, 1.6,0.7,
	RED,          GREEN,       BLUE,
	//1.5,0.0, 1.6,0.7, 1.5,0.7,
	RED,          GREEN,       BLUE,

	//1.6,0.0, 1.9,0.0, 1.9,0.1,
	RED,          GREEN,       BLUE,
	//1.6,0.0, 1.9,0.1, 1.6,0.1,
	RED,          GREEN,       BLUE,

	// O
	//2.0,0.0, 2.1,0.0, 2.1,0.7,
	RED,          GREEN,       BLUE,
	//2.0,0.0, 2.1,0.7, 2.0,0.7,
	RED,          GREEN,       BLUE,

	//2.1,0.0, 2.3,0.0, 2.3,0.1,
	RED,          GREEN,       BLUE,
	//2.1,0.0, 2.3,0.1, 2.1,0.1,
	RED,          GREEN,       BLUE,

	//2.1,0.6, 2.3,0.6, 2.3,0.7,
	RED,          GREEN,       BLUE,
	//2.1,0.6, 2.3,0.7, 2.1,0.7,
	RED,          GREEN,       BLUE,

	//2.3,0.0, 2.4,0.0, 2.4,0.7,
	RED,          GREEN,       BLUE,
	//2.3,0.0, 2.4,0.7, 2.3,0.7,
	RED,          GREEN,       BLUE,

	// E
	//2.5,0.0, 2.6,0.0, 2.6,0.7,
	RED,          GREEN,       BLUE,
	//2.5,0.0, 2.6,0.7, 2.5,0.7,
	RED,          GREEN,       BLUE,

	//2.6,0.0, 2.9,0.0, 2.9,0.1,
	RED,          GREEN,       BLUE,
	//2.6,0.0, 2.9,0.1, 2.6,0.1,
	RED,          GREEN,       BLUE,

	//2.6,0.3, 2.9,0.3, 2.9,0.4,
	RED,          GREEN,       BLUE,
	//2.6,0.3, 2.9,0.4, 2.6,0.4,
	RED,          GREEN,       BLUE,

	//2.6,0.6, 2.9,0.6, 2.9,0.7,
	RED,          GREEN,       BLUE,
	//2.6,0.6, 2.9,0.7, 2.6,0.7,
	RED,          GREEN,       BLUE,

	// G
	//3.1,0.6, 3.4,0.6, 3.4,0.7,
	RED,          GREEN,       BLUE,
	//3.1,0.6, 3.4,0.7, 3.1,0.7,
	RED,          GREEN,       BLUE,

	//3.0,0.0, 3.1,0.0, 3.1,0.7,
	RED,          GREEN,       BLUE,
	//3.0,0.0, 3.1,0.7, 3.0,0.7,
	RED,          GREEN,       BLUE,

	//3.1,0.0, 3.4,0.0, 3.4,0.1,
	RED,          GREEN,       BLUE,
	//3.1,0.0, 3.4,0.1, 3.1,0.1,
	RED,          GREEN,       BLUE,

	//3.3,0.1, 3.4,0.1, 3.4,0.3
	RED,          GREEN,       BLUE,
	//3.3,0.1, 3.4,0.3, 3.3,0.3
	RED,          GREEN,       BLUE,

	//3.25,0.3, 3.45,0.3, 3.45,0.4,
	RED,          GREEN,       BLUE,
	//3.25,0.3, 3.45,0.4, 3.25,0.4,
	RED,          GREEN,       BLUE,

	// L
	//3.5,0.0, 3.6,0.0, 3.6,0.7,
	RED,          GREEN,       BLUE,
	//3.5,0.0, 3.6,0.7, 3.5,0.7,
	RED,          GREEN,       BLUE,

	//3.6,0.0, 3.9,0.0, 3.9,0.1,
	RED,          GREEN,       BLUE,
	//3.6,0.0, 3.9,0.1, 3.6,0.1
	RED,          GREEN,       BLUE
};


#endif // _HELLO_MESH_

可能注意到里面大量调用了宏 Float2Fixed，这是因为 OpenGL ES 1.0 Common Lite Profile 只支持定点数，不能直接使用浮点坐标。所谓定点数这里指的是 16 整数部份 + 16 位小数部份的 32 位数，也就是 OpenGL ES 预定义的 GLfixed 类型。将单精度浮点数转成定点数很简单，直接乘个 65536 再强制一下类型就行了，这也就是 Float2Fixed 所做的。