这段代码捕获OpenGL窗口并将其导出为BMP文件。运行该代码需要安装FreeImage库。
// Make the BYTE array, factor of 3 because it's RBG.
BYTE* pixels = new BYTE[3 * width * height];
glReadPixels(0, 0, width, height, GL_RGB, GL_UNSIGNED_BYTE, pixels);
// Convert to FreeImage format & save to file
FIBITMAP* image = FreeImage_ConvertFromRawBits(pixels, width, height, 3 * width, 24, 0x0000FF, 0xFF0000, 0x00FF00, false);
FreeImage_Save(FIF_BMP, image, "C:/test.bmp", 0);
// Free resources
FreeImage_Unload(image);
delete [] pixels;
glReadPixels 会将数据复制到你提供的内存缓冲区中。在 glReadPixels 返回后,你需要手动将数据格式化(转换为所需的图像格式)并写入磁盘。
fwrite
将数据写入到FILE,fopen
为您提供与指定文件名对应的FILE。但不要忽略有关图像格式的部分,那是棘手的一部分。 - Steve Jessop可运行示例
每次您在窗口上单击鼠标时,都会创建一个名为tmpX.ppm
的文件,其中包含当前截图。
您可以使用Linux上的eog
查看此文件,并使用文本编辑器检查它。
要在不显示窗口的情况下渲染,请参见:如何使用GLUT / OpenGL将内容渲染到文件中?
#include <math.h>
#include <stdlib.h>
#include <stdio.h>
#define GL_GLEXT_PROTOTYPES 1
#include <GL/gl.h>
#include <GL/glu.h>
#include <GL/glut.h>
#include <GL/glext.h>
static GLubyte *pixels = NULL;
static const GLenum FORMAT = GL_RGBA;
static const GLuint FORMAT_NBYTES = 4;
static const unsigned int HEIGHT = 500;
static const unsigned int WIDTH = 500;
static unsigned int nscreenshots = 0;
static unsigned int time;
/* Model. */
static double angle = 0;
static double angle_speed = 45;
static void init(void) {
glReadBuffer(GL_BACK);
glClearColor(0.0, 0.0, 0.0, 0.0);
glPixelStorei(GL_PACK_ALIGNMENT, 1);
glViewport(0, 0, WIDTH, HEIGHT);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glMatrixMode(GL_MODELVIEW);
pixels = malloc(FORMAT_NBYTES * WIDTH * HEIGHT);
time = glutGet(GLUT_ELAPSED_TIME);
}
static void deinit(void) {
free(pixels);
}
static void create_ppm(char *prefix, int frame_id, unsigned int width, unsigned int height,
unsigned int color_max, unsigned int pixel_nbytes, GLubyte *pixels) {
size_t i, j, k, cur;
enum Constants { max_filename = 256 };
char filename[max_filename];
snprintf(filename, max_filename, "%s%d.ppm", prefix, frame_id);
FILE *f = fopen(filename, "w");
fprintf(f, "P3\n%d %d\n%d\n", width, HEIGHT, 255);
for (i = 0; i < height; i++) {
for (j = 0; j < width; j++) {
cur = pixel_nbytes * ((height - i - 1) * width + j);
fprintf(f, "%3d %3d %3d ", pixels[cur], pixels[cur + 1], pixels[cur + 2]);
}
fprintf(f, "\n");
}
fclose(f);
}
static void draw_scene() {
glClear(GL_COLOR_BUFFER_BIT);
glLoadIdentity();
glRotatef(angle, 0.0f, 0.0f, -1.0f);
glBegin(GL_TRIANGLES);
glColor3f(1.0f, 0.0f, 0.0f);
glVertex3f( 0.0f, 0.5f, 0.0f);
glColor3f(0.0f, 1.0f, 0.0f);
glVertex3f(-0.5f, -0.5f, 0.0f);
glColor3f(0.0f, 0.0f, 1.0f);
glVertex3f( 0.5f, -0.5f, 0.0f);
glEnd();
}
static void display(void) {
draw_scene();
glutSwapBuffers();
glReadPixels(0, 0, WIDTH, HEIGHT, FORMAT, GL_UNSIGNED_BYTE, pixels);
}
static void idle(void) {
int new_time = glutGet(GLUT_ELAPSED_TIME);
angle += angle_speed * (new_time - time) / 1000.0;
angle = fmod(angle, 360.0);
time = new_time;
glutPostRedisplay();
}
void mouse(int button, int state, int x, int y) {
if (state == GLUT_DOWN) {
puts("screenshot");
create_ppm("tmp", nscreenshots, WIDTH, HEIGHT, 255, FORMAT_NBYTES, pixels);
nscreenshots++;
}
}
int main(int argc, char **argv) {
GLint glut_display;
glutInit(&argc, argv);
glutInitWindowSize(WIDTH, HEIGHT);
glutInitWindowPosition(100, 100);
glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGBA);
glutCreateWindow(argv[0]);
init();
glutDisplayFunc(display);
glutIdleFunc(idle);
glutMouseFunc(mouse);
atexit(deinit);
glutMainLoop();
return EXIT_SUCCESS;
}
编译方式:
gcc main.c -lm -lGL -lGLU -lglut
将这些数据保存到文件中,你要么自己完成,要么使用第三方库 - OpenGL 没有此功能。
如果你想自己完成,Windows .bmp 格式可能是最简单的 - 维基百科有一个 非常好的文件格式解释。否则,你可以使用图像保存/加载库:libpng、libjpeg 等进行低级控制,或者 devIL(还有其他选择,但这是我最喜欢的,它是一个极其通用的库,与 GL 配合得很好)进行高级“只需操作”图像 i/o。
一个简单快速的解决方案。
tga
文件扩展名。以下是代码:
void saveScreenshotToFile(std::string filename, int windowWidth, int windowHeight) {
const int numberOfPixels = windowWidth * windowHeight * 3;
unsigned char pixels[numberOfPixels];
glPixelStorei(GL_PACK_ALIGNMENT, 1);
glReadBuffer(GL_FRONT);
glReadPixels(0, 0, windowWidth, windowHeight, GL_BGR_EXT, GL_UNSIGNED_BYTE, pixels);
FILE *outputFile = fopen(filename.c_str(), "w");
short header[] = {0, 2, 0, 0, 0, 0, (short) windowWidth, (short) windowHeight, 24};
fwrite(&header, sizeof(header), 1, outputFile);
fwrite(pixels, numberOfPixels, 1, outputFile);
fclose(outputFile);
printf("Finish writing to file.\n");
}
并调用该函数:
saveScreenshotToFile("test.tga", 1200, 900);
for oldFileName in *.tga; do
[ -f "$oldFileName" ] || break # Break out if no .tga files found.
newFileName=${oldFileName//.tga/.png}
convert $oldFileName $newFileName
rm $oldFileName
echo "Converted $oldFileName to $newFileName"
done
您可以使用@Rafael的答案和OpenCV保存屏幕截图:
void Game::saveScreenshotToFile(std::string filename, int windowWidth, int windowHeight) {
cv::Mat img(windowHeight, windowWidth, CV_8UC3);
glPixelStorei(GL_PACK_ALIGNMENT, (img.step & 3) ? 1 : 4);
glPixelStorei(GL_PACK_ROW_LENGTH, img.step/img.elemSize());
glReadPixels(0, 0, img.cols, img.rows, GL_BGR, GL_UNSIGNED_BYTE, img.data);
cv::flip(img, img, 0);
//cv::imshow("Image",img);
//cv::waitKey(0);
cv::imwrite(filename, img);
}
一般来说,OpenGL没有提供保存图像的函数。我认为最快捷、最简单的方法是保存成PPM格式。然而,这种格式未经压缩,意味着文件大小会很大,现在也只能被少数程序支持。
我更喜欢将图像保存为压缩的.png文件,这样可以保证无损图像,并且得到许多浏览器的支持。要将OpenGL保存为.png格式,我首先推荐使用PNGwriter。它非常简单易用。例如,要保存一个位置为(x,y)具有颜色(R,G,B)的像素,请参阅PNGwriter网站上的“快速入门”:
pngwriter PNG(width, height, 1.0, fileName); // "1.0" stand for the white background
PNG.plot(x, y, R, G, B);
PNG.close();
请注意,PNGwriter 从图像的左上角开始保存每个像素,而从 glReadPixels() 获取的数组则从窗口的左下角开始。因此,保存整个图像的代码可能如下所示:
GLfloat* pixels = new GLfloat[nPixels];
glReadPixels(0.0, 0.0, width, height,GL_RGB, GL_FLOAT, pixels);
pngwriter PNG(width, height, 1.0, fileName);
size_t x = 1;
size_t y = 1;
double R, G, B;
for(size_t i=0; i<npixels; i++) // "i" is the index for array "pixels"
{
switch(i%3)
{
case 2:
B = static_cast<double>(pixels[i]); break;
case 1:
G = static_cast<double>(pixels[i]); break;
case 0:
R = static_cast<double>(pixels[i]);
PNG.plot(x, y, R, G, B); // set pixel to position (x, y)
if( x == width ) // Move to the next row of image
{
x=1;
y++;
}
else // To the next pixel
{ x++; }
break;
}
}
PNG.close();
GL_UNSIGNED_BYTE
来代替Windows特定的BYTE
来表示该数组。 - RiotGLubyte
。 - RiotGL_PACK_ALIGNMENT
会更好,因为glReadPixels
正在打包而不是解包 :) - vallentin