Linux之X11+OpenGL+EGL绘制(二十)，这些面试官常问的开发面试题你都掌握好了吗

• atan(pos.y,pos.x) - phase ); \

} \

";

// handle to the shader

void print_shader_info_log (GLuint shader){

GLint length;

glGetShaderiv ( shader , GL_INFO_LOG_LENGTH , &length );

if ( length ) {

char* buffer = new char [ length ];

glGetShaderInfoLog ( shader , length , NULL , buffer );

cout << "shader info: " << buffer << flush;

delete [] buffer;

GLint success;

glGetShaderiv( shader, GL_COMPILE_STATUS, &success );

if ( success != GL_TRUE ) exit ( 1 );

}

}

GLuint load_shader ( const char *shader_source, GLenum type){

GLuint shader = glCreateShader( type );

glShaderSource ( shader , 1 , &shader_source , NULL );

glCompileShader ( shader );

print_shader_info_log ( shader );

return shader;

}

Display *x_display;

Window win;

EGLDisplay egl_display;

EGLContext egl_context;

EGLSurface egl_surface;

GLfloat

norm_x = 0.0,

norm_y = 0.0,

offset_x = 0.0,

offset_y = 0.0,

p1_pos_x = 0.0,

p1_pos_y = 0.0;

GLint phase_loc, offset_loc, position_loc;

bool update_pos = false;

const float vertexArray[] = {

0.0, 0.5, 0.0,

-0.5, 0.0, 0.0,

0.0, -0.5, 0.0,

0.5, 0.0, 0.0,

0.0, 0.5, 0.0

};

void render(){

static float phase = 0;

static int donesetup = 0;

static XWindowAttributes gwa;

draw

if ( !donesetup ) {

XWindowAttributes gwa;

XGetWindowAttributes ( x_display , win , &gwa );

glViewport ( 0 , 0 , gwa.width , gwa.height );

glClearColor ( 0.08 , 0.06 , 0.07 , 1.); // background color

donesetup = 1;

}

glClear ( GL_COLOR_BUFFER_BIT );

glUniform1f ( phase_loc , phase ); // write the value of phase to the shaders phase

phase = fmodf ( phase + 0.5f , 2.f * 3.141f ); // and update the local variable

if ( update_pos ) { // if the position of the texture has changed due to user action

GLfloat old_offset_x = offset_x;

GLfloat old_offset_y = offset_y;

offset_x = norm_x - p1_pos_x;

offset_y = norm_y - p1_pos_y;

p1_pos_x = norm_x;

p1_pos_y = norm_y;

offset_x += old_offset_x;

offset

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_y += old_offset_y;

update_pos = false;

}

glUniform4f ( offset_loc , offset_x , offset_y , 0.0 , 0.0 );

glVertexAttribPointer ( position_loc, 3, GL_FLOAT, false, 0, vertexArray );

glEnableVertexAttribArray ( position_loc );

glDrawArrays ( GL_TRIANGLE_STRIP, 0, 5 );

eglSwapBuffers ( egl_display, egl_surface ); // get the rendered buffer to the screen

}

int main(){

/// the X11 part //

// in the first part the program opens a connection to the X11 window manager

//

x_display = XOpenDisplay ( NULL ); // open the standard display (the primary screen)

if ( x_display == NULL ) {

cerr << “cannot connect to X server” << endl;

return 1;

}

Window root = DefaultRootWindow( x_display ); // get the root window (usually the whole screen)

XSetWindowAttributes swa;

swa.event_mask = ExposureMask | PointerMotionMask | KeyPressMask;

win = XCreateWindow ( // create a window with the provided parameters

x_display, root,

0, 0, 800, 480, 0,

CopyFromParent, InputOutput,

CopyFromParent, CWEventMask,

&swa );

XSetWindowAttributes xattr;

Atom atom;

int one = 1;

xattr.override_redirect = False;

XChangeWindowAttributes ( x_display, win, CWOverrideRedirect, &xattr );

atom = XInternAtom ( x_display, “_NET_WM_STATE_FULLSCREEN”, True );

XChangeProperty (

x_display, win,

XInternAtom ( x_display, “_NET_WM_STATE”, True ),

XA_ATOM, 32, PropModeReplace,

(unsigned char*) &atom, 1 );

XChangeProperty (

x_display, win,

XInternAtom ( x_display, “_HILDON_NON_COMPOSITED_WINDOW”, False ),

XA_INTEGER, 32, PropModeReplace,

(unsigned char*) &one, 1);

XWMHints hints;

hints.input = True;

hints.flags = InputHint;

XSetWMHints(x_display, win, &hints);

XMapWindow ( x_display , win ); // make the window visible on the screen

XStoreName ( x_display , win , “GL test” ); // give the window a name

get identifiers for the provided atom name strings

Atom wm_state = XInternAtom ( x_display, “_NET_WM_STATE”, False );

Atom fullscreen = XInternAtom ( x_display, “_NET_WM_STATE_FULLSCREEN”, False );

XEvent xev;

memset ( &xev, 0, sizeof(xev) );

xev.type = ClientMessage;

xev.xclient.window = win;

xev.xclient.message_type = wm_state;

xev.xclient.format = 32;

xev.xclient.data.l[0] = 1;

xev.xclient.data.l[1] = fullscreen;

XSendEvent ( // send an event mask to the X-server

x_display,

DefaultRootWindow ( x_display ),

False,

SubstructureNotifyMask,

&xev );

/// the egl part //

// egl provides an interface to connect the graphics related functionality of openGL ES

// with the windowing interface and functionality of the native operation system (X11

// in our case.

egl_display = eglGetDisplay( (EGLNativeDisplayType) x_display );

if ( egl_display == EGL_NO_DISPLAY ) {

cerr << “Got no EGL display.” << endl;

return 1;

}

if ( !eglInitialize( egl_display, NULL, NULL ) ) {

cerr << “Unable to initialize EGL” << endl;

return 1;

}

EGLint attr[] = { // some attributes to set up our egl-interface

EGL_BUFFER_SIZE, 16,

EGL_RENDERABLE_TYPE,

EGL_OPENGL_ES2_BIT,

EGL_NONE

};

EGLConfig ecfg;

EGLint num_config;

if ( !eglChooseConfig( egl_display, attr, &ecfg, 1, &num_config ) ) {

cerr << "Failed to choose config (eglError: " << eglGetError() << “)” << endl;

return 1;

}

if ( num_config != 1 ) {

cerr << "Didn’t get exactly one config, but " << num_config << endl;

return 1;

}

egl_surface = eglCreateWindowSurface ( egl_display, ecfg, win, NULL );

if ( egl_surface == EGL_NO_SURFACE ) {

cerr << "Unable to create EGL surface (eglError: " << eglGetError() << “)” << endl;

return 1;

}

egl-contexts collect all state descriptions needed required for operation

EGLint ctxattr[] = {

EGL_CONTEXT_CLIENT_VERSION, 2,

EGL_NONE

};

egl_context = eglCreateContext ( egl_display, ecfg, EGL_NO_CONTEXT, ctxattr );

if ( egl_context == EGL_NO_CONTEXT ) {

cerr << "Unable to create EGL context (eglError: " << eglGetError() << “)” << endl;

return 1;

}

associate the egl-context with the egl-surface

eglMakeCurrent( egl_display, egl_surface, egl_surface, egl_context );

/// the openGL part ///

GLuint vertexShader = load_shader ( vertex_src , GL_VERTEX_SHADER ); // load vertex shader

GLuint fragmentShader = load_shader ( fragment_src , GL_FRAGMENT_SHADER ); // load fragment shader

GLuint shaderProgram = glCreateProgram (); // create program object

glAttachShader ( shaderProgram, vertexShader ); // and attach both…

glAttachShader ( shaderProgram, fragmentShader ); // … shaders to it

glLinkProgram ( shaderProgram ); // link the program

glUseProgram ( shaderProgram ); // and select it for usage

now get the locations (kind of handle) of the shaders variables

position_loc = glGetAttribLocation ( shaderProgram , “position” );

phase_loc = glGetUniformLocation ( shaderProgram , “phase” );

offset_loc = glGetUniformLocation ( shaderProgram , “offset” );

if ( position_loc < 0 || phase_loc < 0 || offset_loc < 0 ) {

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来源： https://blog.csdn.net/m0_65146387/article/details/122027537