将OpenGL代码移植成OpenGLES
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将OpenGL代码移植成OpenGLES
http://blog.csdn.net/langresser_king/article/details/7891278
首先是一些基础概念和经验分享:
1、OpenGL是一个跨平台的图形渲染标准
2、OpenGL ES (OpenGL for Embedded Systems) 是 OpenGL 三维图形 API 的子集,针对手机、PDA和游戏主机等嵌入式设备而设计。该API由Khronos集团定义推广,Khronos是一个图形软硬件行业协会,该协会主要关注图形和多媒体方面的开放标准。
OpenGL ES 是从 OpenGL 裁剪定制而来的,去除了 glBegin/glEnd,四边形(GL_QUADS)、多边形(GL_POLYGONS)等复杂图元等许多非绝对必要的特性。现在主要有两个版本,OpenGL ES 1.1针对固定管线硬件的,是以 OpenGL 1.5 规范为基础的。OpenGL ES 2.x 针对可编程管线硬件,参照 OpenGL 2.0 规范定义。
3、egl提供了opengles和本地窗口之间的关联
4、OpenGLES模拟器,这里的模拟器仅仅是一套api和dll(要与android模拟器区分开)。主要用于非嵌入式平台(如windows)下运行opengles代码。
============================================正文==============================================================
1、头文件:
- #if !defined(HAVE_GLES)
- #include <GL/gl.h>
- #else
- #include <GLES/gl.h>
- #endif
2、windows下可以使用eglport(http://sourceforge.net/p/eglport/code-0/3/tree/trunk/),android和ios下各有其对应实现,如果使用了SDL的话,基础框架如下:
- #if !defined(HAVE_GLES)
- #include <GL/gl.h>
- #else
- #include <GLES/gl.h>
- #include "eglport.h"
- #endif
- #include <SDL/SDL.h>
- int main( void )
- {
- // other stuff here
- SDL_Init( SDL_INIT_VIDEO );
- #if defined(HAVE_GLES)
- if (EGL_Open())
- exit(1);
- #endif
- // some more initialisations
- SDL_Surface* screen;
- #if !defined(HAVE_GLES)
- screen = SDL_SetVideoMode( 800, 600, 0, SDL_HWSURFACE | SDL_OPENGL | SDL_FULLSCREEN);
- #else
- screen = SDL_SetVideoMode( 800, 480, 0, SDL_SWSURFACE | SDL_FULLSCREEN );
- EGL_Init();
- #endif
- // the event loop
- while( quit == 0 ) {
- // management of the even and the game
- #if !defined(HAVE_GLES)
- SDL_GL_SwapBuffers();
- #else
- EGL_SwapBuffers();
- #endif
- }
- // probably some more clean-ups here
- #if defined(HAVE_GLES)
- EGL_Close();
- #endif
- SDL_Quit();
- return 0;
- }
注意EGL_xxx系列函数的位置。
3、一些宏定义:
gles只支持浮点型
- #define GLdouble GLfloat
- #define GL_CLAMP GL_CLAMP_TO_EDGE
- #define glClearDepth glClearDepthf
- #define glOrtho glOrthof
- #define glFrustum glFrustumf
- #define glColor4fv(a) glColor4f(a[0], a[1], a[2], a[3])
- #define glColor3fv(a) glColor4f(a[0], a[1], a[2], 1.0f)
- #define glColor3f(a,b,c) glColor4f(a, b, c, 1.0f)
4、具体代码移植示例,因为gles去除了glBegin等函数,所以贴图、顶点绘制、画线等代码都有可能需要进行修改
a、没有颜色的普通矩形:
- #if !defined(HAVE_GLES)
- glBegin(GL_QUADS);
- glVertex2f(-10,-10);
- glVertex2f(10,-10);
- glVertex2f(10,10);
- glVertex2f(-10,10);
- glEnd();
- #else
- GLfloat q3[] = {
- -10,-10,
- 10,-10,
- 10,10,
- -10,10
- };
- glEnableClientState(GL_VERTEX_ARRAY);
- glVertexPointer(2, GL_FLOAT, 0, q3);
- glDrawArrays(GL_TRIANGLE_FAN,0,4);
- glDisableClientState(GL_VERTEX_ARRAY);
- #endif
b、贴图
- glBindTexture(GL_TEXTURE_2D, carac->TextureName);
- #if !defined(HAVE_GLES)
- glBegin(GL_QUADS);
- glTexCoord2f(0,0);
- glVertex3f(pos[0]-tailleX/2, pos[1]-tailleY/2, 0);
- glTexCoord2f(1,0);
- glVertex3f(pos[0]+tailleX/2, pos[1]-tailleY/2, 0);
- glTexCoord2f(1,1);
- glVertex3f(pos[0]+tailleX/2, pos[1]+tailleY/2, 0);
- glTexCoord2f(0,1);
- glVertex3f(pos[0]-tailleX/2, pos[1]+tailleY/2, 0);
- glEnd();
- #else
- GLfloat vtx1[] = {
- pos[0]-tailleX/2, pos[1]-tailleY/2, 0,
- pos[0]+tailleX/2, pos[1]-tailleY/2, 0,
- pos[0]+tailleX/2, pos[1]+tailleY/2, 0,
- pos[0]-tailleX/2, pos[1]+tailleY/2, 0
- };
- GLfloat tex1[] = {
- 0,0,
- 1,0,
- 1,1,
- 0,1
- };
- glEnableClientState(GL_VERTEX_ARRAY);
- glEnableClientState(GL_TEXTURE_COORD_ARRAY);
- glVertexPointer(3, GL_FLOAT, 0, vtx1);
- glTexCoordPointer(2, GL_FLOAT, 0, tex1);
- glDrawArrays(GL_TRIANGLE_FAN,0,4);
- glDisableClientState(GL_VERTEX_ARRAY);
- glDisableClientState(GL_TEXTURE_COORD_ARRAY);
- #endif
c、颜色渐变:
- #if !defined(HAVE_GLES)
- glBegin(GL_QUADS);
- glColor3d( .1, .1, .7);
- glVertex3d(0, 0, 0);
- glVertex3d(0, -pbarheight, 0);
- glColor3d( 0, 0, 0.5);
- glVertex3d((startupProgress / startupProgressSteps) * pbarwidth, -pbarheight, 0);
- glVertex3d((startupProgress / startupProgressSteps) * pbarwidth, 0, 0);
- glEnd();
- #else
- GLfloat vtx1[] = {
- 0, 0, 0,
- 0, -pbarheight, 0,
- (startupProgress / startupProgressSteps) * pbarwidth, -pbarheight, 0,
- (startupProgress / startupProgressSteps) * pbarwidth, 0, 0
- };
- GLfloat col1[] = {
- .1, .1, .7, 1.0f,
- .1, .1, .7, 1.0f,
- 0, 0, 0.5, 1.0f,
- 0, 0, 0.5, 1.0f
- };
- glEnableClientState(GL_VERTEX_ARRAY);
- glEnableClientState(GL_COLOR_ARRAY);
- glVertexPointer(3, GL_FLOAT, 0, vtx1);
- glColorPointer(4, GL_FLOAT, 0, col1);
- glDrawArrays(GL_TRIANGLE_FAN,0,4);
- glDisableClientState(GL_COLOR_ARRAY);
- glDisableClientState(GL_VERTEX_ARRAY);
- #endif
d、三角形扇面:
- #if !defined(HAVE_GLES)
- glBegin(GL_QUAD_STRIP);
- // Front
- glVertex3f(-left, 0, front); // bottom left
- glVertex3f(-left-wider, height, front+wider); // top left
- glVertex3f( right, 0, front); // bottom right
- glVertex3f( right+wider, height, front+wider); // top right
- // Right
- glVertex3f( right, 0,-back); // bottom r
- glVertex3f( right+wider, height,-back-wider); // top r
- // Back
- glVertex3f(-left, 0, -back); // bottom right
- glVertex3f(-left-wider, height, -back-wider); // top right
- // Left
- glVertex3f(-left, 0, front); // bottom r
- glVertex3f(-left-wider, height, front+wider); // top r
- glEnd();
- #else
- {
- GLfloat vtx1[] = {-left, 0, front, -left-wider, height, front+wider, right, 0, front, right+wider, height, front+wider};
- GLfloat vtx2[] = {right, 0, front, right+wider, height, front+wider, right, 0,-back, right+wider, height,-back-wider};
- GLfloat vtx3[] = {right, 0,-back, right+wider, height,-back-wider, -left, 0, -back, -left-wider, height, -back-wider};
- GLfloat vtx4[] = {-left, 0, -back, -left-wider, height, -back-wider, -left, 0, front, -left-wider, height, front+wider};
- glEnableClientState(GL_VERTEX_ARRAY);
- glVertexPointer(3, GL_FLOAT, 0, vtx1);
- glDrawArrays(GL_TRIANGLE_FAN,0,4);
- glVertexPointer(3, GL_FLOAT, 0, vtx2);
- glDrawArrays(GL_TRIANGLE_FAN,0,4);
- glVertexPointer(3, GL_FLOAT, 0, vtx3);
- glDrawArrays(GL_TRIANGLE_FAN,0,4);
- glVertexPointer(3, GL_FLOAT, 0, vtx4);
- glDrawArrays(GL_TRIANGLE_FAN,0,4);
- glDisableClientState(GL_VERTEX_ARRAY);
- }
- #endif
e、使用int/short
- #if !defined(HAVE_GLES)
- glBegin(GL_QUADS);
- glTexCoord2i(0, 1); glVertex2i(-256, -256);
- glTexCoord2i(0, 0); glVertex2i(-256, 256);
- glTexCoord2i(1, 0); glVertex2i(256, 256);
- glTexCoord2i(1, 1); glVertex2i(256, -256);
- glEnd();
- #else
- GLshort vtx1[] = { -256, -256, -256, 256, 256, 256, 256, -256 };
- GLshort tex1[] = { 0, 1, 0, 0, 1, 0, 1, 1 };
- glEnableClientState(GL_VERTEX_ARRAY);
- glEnableClientState(GL_TEXTURE_COORD_ARRAY);
- glVertexPointer(2, GL_SHORT, 0, vtx1);
- glTexCoordPointer(2, GL_SHORT, 0, tex1);
- glDrawArrays(GL_TRIANGLE_FAN,0,4);
- glDisableClientState(GL_VERTEX_ARRAY);
- glDisableClientState(GL_TEXTURE_COORD_ARRAY);
- #endif
f、glRect
- #ifndef HAVE_GLES
- glRecti ( dx + min[0], dy + min[1],
- dx + max[0], dy + max[1] ) ;
- #else
- GLshort vtx1[] = { dx + min[0], dy + min[1], dx + min[0], dy + max[1], dx + max[0], dy + max[1], dx + max[0], dy + min[1]};
- glEnableClientState(GL_VERTEX_ARRAY);
- glVertexPointer(2, GL_SHORT, 0, vtx1);
- glDrawArrays(GL_TRIANGLE_FAN,0,4);
- glDisableClientState(GL_VERTEX_ARRAY);
- #endif
5、glDrawArrays渲染模式对应关系
- GL_POINTS -> GL_POINTS
- GL_TRIANGLES -> GL_TRIANGLES (or GL_LINE_LOOP if glPolygonMode is set to GL_LINE)
- GL_QUADS -> GL_TRIANGLE_FAN
- GL_LINE_STRIP -> GL_LINE_STRIP
- GL_LINE -> GL_LINE
- GL_POLYGON -> GL_TRIANGLE_FAN
6、所有贴图必须是2的整次幂,某些特殊情况会有更高的需求(如powervr显卡使用pvr贴图必须是正方形以及2的整次幂大小)。
- 将OpenGL代码移植成OpenGLES
- 将OpenGL代码移植成OpenGLES
- 将OpenGL代码移植成OpenGLES
- 将OpenGL代码移植成OpenGLES
- 将OpenGL代码移植成OpenGL ES
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