Raspberry Pi（树莓派）基于Raspbian操作系统开发OpenGL ES应用 |
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笔者在树莓派上开发OpenGL ES之前，特地从网上做了些功课。当前，无论是Raspberry Pi 3还是Zero，倘若要开启博通的Video Core GPU硬件加速，那么只能使用官方提供的 Raspbian OS 系统，并且需要使用存放在 /opt/vc/ 下的私有库。因此，我们只能通过EGL结合树莓派特定的DispManX运行时环境来使用OpenGL ES。在 /opt/vc/src/hello_pi/ 目录下放有官方提供的各种demo，其中包括OpenGL ES程序、OpenVG程序以及利用Video Core硬件视频编解码能力对视频进行处理的demo等。 由于 /opt/vc/lib/ 目录下已经包含了OpenGL ES所需要的所有基本库，包括OpenGL ES以及EGL的实现等，因此我们无需再使用 apt-get 去下载安装其他OpenGL ES相关的库了。其中，bcm_host这个库就是博通公司私有的、用于驱动Video Core GPU的库，并且要在使用Video Core GPU之前，必须调用 bcm_host_init 这个函数。 方便起见，笔者做了一个编译shell文件，名为 build.sh。其内容如下： gcc main.c -o rectangle -std=gnu11 -DSTANDALONE -D__STDC_CONSTANT_MACROS -D__STDC_LIMIT_MACROS -DTARGET_POSIX -D_LINUX -D_REENTRANT -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -U_FORTIFY_SOURCE -Wall -g -DHAVE_LIBOPENMAX=2 -DOMX -DOMX_SKIP64BIT -ftree-vectorize -pipe -DUSE_EXTERNAL_OMX -DHAVE_LIBBCM_HOST -DUSE_EXTERNAL_LIBBCM_HOST -DUSE_VCHIQ_ARM -Wno-psabi -L/opt/vc/lib/ -lbrcmGLESv2 -lbrcmEGL -lopenmaxil -lbcm_host -lvcos -lvchiq_arm -lpthread -lrt -lm -L/opt/vc/src/hello_pi/libs/ilclient -L/opt/vc/src/hello_pi/libs/vgfont -I/opt/vc/include/ -I/opt/vc/include/interface/vcos/pthreads -I/opt/vc/include/interface/vmcs_host/linux -I./ -I/opt/vc/src/hello_pi/libs/ilclient -I/opt/vc/src/hello_pi/libs/vgfont各位在使用时，只需要把源文件名 main.c 以及 rectangle 这一输出文件名进行修改即可，其他都不需要动。我们编辑好main.c源文件之后，直接用 bash build.sh 这个编译脚本即可。 下面给出main.c的代码： #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include static EGL_DISPMANX_WINDOW_T sNativewindow; static DISPMANX_DISPLAY_HANDLE_T sDispmanDisplay; static DISPMANX_ELEMENT_HANDLE_T sDispmanElement; static EGLDisplay sDisplay; static EGLSurface sSurface; static EGLContext sContext; static uint32_t screen_width = 0, screen_height = 0; /// Object rotation angle static int sRotateAngle = 0; /// Indicate whether animation should be paused static bool sShouldPauseAnimation = false; /// Indicate whether the current program should exit the message run loop. static bool sShouldTerminate = false; /// Rectangle vertex coordinates static const GLfloat sRectVertices[] = { // top left -0.4f, 0.4f, // bottom left -0.4f, -0.4f, // top right 0.4f, 0.4f, // bottom right 0.4f, -0.4f }; /// Triangle vertex coordinates static const GLfloat sTriangleVertices[] = { // top left 0.0f, 0.4f, // bottom left -0.4f, -0.4f, // bottom right 0.4f, -0.4f }; static const GLfloat sColors[] = { // red 1.0f, 0.0f, 0.0f, 1.0f, // green 0.0f, 1.0f, 0.0f, 1.0f, // blue 0.0f, 0.0f, 1.0f, 1.0f, // white 1.0f, 1.0f, 1.0f, 1.0f }; /// Setup OpenGL ES context and the models static void SetupOGLStates(void) { glViewport(0, 0, screen_width, screen_height); // Set background color and clear buffers glClearColor(0.15f, 0.25f, 0.35f, 1.0f); // Use smooth shade model, which is the default configuration glShadeModel(GL_SMOOTH); // Config the front face is in the counter clock-wise direction glFrontFace(GL_CCW); // Cull the back faces glCullFace(GL_BACK); // Enable back face culling. glEnable(GL_CULL_FACE); glEnableClientState(GL_VERTEX_ARRAY); glEnableClientState(GL_COLOR_ARRAY); // Setup projection transformation glMatrixMode(GL_PROJECTION); glLoadIdentity(); float scale; if(screen_width scale = (float)screen_height / (float)screen_width; glOrthof(-1.0f, 1.0f, -scale, scale, 1.0f, 3.0f); } // The following steps are based on model view transformation glMatrixMode(GL_MODELVIEW); } /// EGL attribute list for context configuration static const EGLint attribute_list[] = { EGL_RED_SIZE, 8, EGL_GREEN_SIZE, 8, EGL_BLUE_SIZE, 8, EGL_ALPHA_SIZE, 8, EGL_SURFACE_TYPE, EGL_WINDOW_BIT, // In this demo, use OpenGL ES 1.x version EGL_RENDERABLE_TYPE, EGL_OPENGL_ES_BIT, // We will use multisample anti-aliasing EGL_SAMPLE_BUFFERS, 1, // Here specifies 4x samples EGL_SAMPLES, 4, // config complete EGL_NONE }; /// Initialize the EGL context and do some other OpenGL ES configuration static void InitializeEGLContext(void) { // get an EGL display connection sDisplay = eglGetDisplay(EGL_DEFAULT_DISPLAY); assert(sDisplay != EGL_NO_DISPLAY); // initialize the EGL display connection EGLBoolean result = eglInitialize(sDisplay, NULL, NULL); assert(EGL_FALSE != result); // get an appropriate EGL frame buffer configuration EGLConfig config; EGLint num_config; result = eglChooseConfig(sDisplay, attribute_list, &config, 1, &num_config); assert(EGL_FALSE != result); // create an EGL rendering context sContext = eglCreateContext(sDisplay, config, EGL_NO_CONTEXT, NULL); assert(sContext != EGL_NO_CONTEXT); // create an EGL window surface int success = graphics_get_display_size(0 /* LCD */, &screen_width, &screen_height); assert( success >= 0 ); printf("Current screen resolution: %ux%u\n", screen_width, screen_height); VC_RECT_T dst_rect; dst_rect.x = 0; dst_rect.y = 0; dst_rect.width = screen_width; dst_rect.height = screen_height; VC_RECT_T src_rect; src_rect.x = 0; src_rect.y = 0; src_rect.width = screen_width if(++sRotateAngle == 360) sRotateAngle = 0; } eglSwapBuffers(sDisplay, sSurface); } static void DestroyEGLContext(void) { DISPMANX_UPDATE_HANDLE_T dispman_update; // clear screen glClear( GL_COLOR_BUFFER_BIT ); eglSwapBuffers(sDisplay, sSurface); eglDestroySurface(sDisplay, sSurface); dispman_update = vc_dispmanx_update_start( 0 ); int s = vc_dispmanx_element_remove(dispman_update, sDispmanElement); assert(s == 0); vc_dispmanx_update_submit_sync( dispman_update ); s = vc_dispmanx_display_close(sDispmanDisplay); assert (s == 0); // Release OpenGL resources eglMakeCurrent(sDisplay, EGL_NO_SURFACE, EGL_NO_SURFACE, EGL_NO_CONTEXT ); eglDestroyContext(sDisplay, sContext); eglTerminate(sDisplay); } /// File handle for keyboard events static int stdin_fd = -1; static struct termios sTermOriginal; /// Fetch the character if there's any key is pressed. /// @return If any key is pressed, return the relevant character; Otherwise, return -1. static int KeyPressed(void) { // If this is the first time the function is called, change the stdin // stream so that we get each character when the keys are pressed and // and so that character aren't echoed to the screen when the keys are // pressed. if (stdin_fd == -1) { // Get the file descriptor associated with stdin stream. stdin_fd = fileno(stdin); // Get the terminal (termios) attritubets for stdin so we can // modify them and reset them before exiting the program. tcgetattr(stdin_fd, &sTermOriginal); // Copy the termios attributes so we can modify them. struct termios term; memcpy(&term, &sTermOriginal, sizeof(term)); // Unset ICANON and ECHO for stdin. When ICANON is not set the // input is in noncanonical mode. In noncanonical mode input is // available as each key is pressed. In canonical mode input is // only available after the enter key is pressed. Unset ECHO so that // the characters aren't echoed to the screen when keys are pressed. // See the termios(3) man page for more information. term.c_lflag &= ~(ICANON|ECHO); tcsetattr(stdin_fd, TCSANOW, &term); // Turn off buffering for stdin. We want to get the characters // immediately. We don't want the characters to be buffered. setbuf(stdin, NULL); } int character = -1; // Get the number of characters that are waiting to be read. int characters_buffered = 0; ioctl(stdin_fd, FIONREAD, &characters_buffered); if (characters_buffered == 1) { // There is only one character to be read. Read it in. character = fgetc(stdin); } else if (characters_buffered > 1) { // There is more than one character to be read. // In this situation, just get the last read character while (characters_buffered != 0) { character = fgetc(stdin); --characters_buffered; } } return character; } /// If keyPressed() has been called, /// the terminal input has been changed for the stdin stream. /// Put the attributes back the way we found them. static void KeyboardReset(void) { if(stdin_fd != -1) tcsetattr(stdin_fd, TCSANOW, &sTermOriginal); } //============================================================================== int main (void) { // Initialize VideoCore GPU bcm_host_init(); InitializeEGLContext(); SetupOGLStates(); while (!sShouldTerminate) { redraw_scene(); const int code = KeyPressed(); if(code == 0x20) sShouldPauseAnimation = !sShouldPauseAnimation; sShouldTerminate = code == '\n' || code == 0x1b; } KeyboardReset(); DestroyEGLContext(); puts("\nApplication closed"); return 0; }在这个demo中，我们必须通过命令行来开启，否则它无法侦听键盘按键消息。我们按下回车或ESC退出程序，按下空格暂停旋转动画。 |
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