如何使用GLUT/OpenGL渲染到文件?
我有一个程序,模拟一个随时间变化的物理系统。我想以预定的间隔(比如每10秒)将模拟状态的可视化输出到一个文件中。我想这样做,它很容易“关闭可视化”,而根本不输出可视化如何使用GLUT/OpenGL渲染到文件?,opengl,graphics,visualization,glut,Opengl,Graphics,Visualization,Glut,我有一个程序,模拟一个随时间变化的物理系统。我想以预定的间隔(比如每10秒)将模拟状态的可视化输出到一个文件中。我想这样做,它很容易“关闭可视化”,而根本不输出可视化 我将OpenGL和GLUT作为图形工具来进行可视化。然而问题似乎是,首先,它看起来只输出到窗口,而不能输出到文件。其次,为了生成可视化,您必须调用GLUTMainLoop并停止主函数的执行-从那时起,唯一被调用的函数是来自GUI的调用。但是,我不希望它是一个基于GUI的应用程序——我希望它只是一个从命令行运行的应用程序,它会生成一
我将OpenGL和GLUT作为图形工具来进行可视化。然而问题似乎是,首先,它看起来只输出到窗口,而不能输出到文件。其次,为了生成可视化,您必须调用GLUTMainLoop并停止主函数的执行-从那时起,唯一被调用的函数是来自GUI的调用。但是,我不希望它是一个基于GUI的应用程序——我希望它只是一个从命令行运行的应用程序,它会生成一系列图像。在GLUT/OpenGL中有这样做的方法吗?或者OpenGL完全是一个错误的工具,我应该使用其他工具不确定OpenGL是否是最好的解决方案。
但您始终可以渲染到屏幕外缓冲区
将openGL输出写入文件的典型方法是使用readPixels将生成的场景像素复制到图像文件中无论如何,您几乎肯定不需要GLUT。您的需求不符合预期目标(即使您的需求符合预期目标,您通常也不会想要它) 您可以使用OpenGL。要在文件中生成输出,基本上需要将OpenGL设置为渲染到纹理,然后将生成的纹理读入主内存并保存到文件中。至少在某些系统(例如Windows)上,我敢肯定您仍然需要创建一个窗口并将渲染上下文与该窗口关联,尽管如果该窗口总是隐藏的,这可能会很好。您可以使用SFML。可以使用image类保存渲染输出 要获得渲染输出,可以渲染到纹理或复制屏幕 渲染到纹理:
glReadPixels
可运行PBO示例
下面的示例生成以下两种情况之一:
- 200 FPS时每帧1 ppm,无额外依赖性
- 每帧一个png,每秒600帧,带libpng
- 使用FFmpeg以1200 FPS的速度为所有帧提供一个mpg
glReadPixels
是从屏幕读取像素的关键OpenGL函数。还可以查看init()
下的设置
glReadPixels
与大多数图像格式不同,首先读取像素的底线,因此通常需要进行转换
屏幕外
#ifndef PPM
#define PPM 1
#endif
#ifndef LIBPNG
#define LIBPNG 1
#endif
#ifndef FFMPEG
#define FFMPEG 1
#endif
#include <assert.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define GL_GLEXT_PROTOTYPES 1
#include <GL/gl.h>
#include <GL/glu.h>
#include <GL/glut.h>
#include <GL/glext.h>
#if LIBPNG
#include <png.h>
#endif
#if FFMPEG
#include <libavcodec/avcodec.h>
#include <libavutil/imgutils.h>
#include <libavutil/opt.h>
#include <libswscale/swscale.h>
#endif
enum Constants { SCREENSHOT_MAX_FILENAME = 256 };
static GLubyte *pixels = NULL;
static GLuint fbo;
static GLuint rbo_color;
static GLuint rbo_depth;
static int offscreen = 1;
static unsigned int max_nframes = 128;
static unsigned int nframes = 0;
static unsigned int time0;
static unsigned int height = 128;
static unsigned int width = 128;
#define PPM_BIT (1 << 0)
#define LIBPNG_BIT (1 << 1)
#define FFMPEG_BIT (1 << 2)
static unsigned int output_formats = PPM_BIT | LIBPNG_BIT | FFMPEG_BIT;
/* Model. */
static double angle;
static double delta_angle;
#if PPM
/* Take screenshot with glReadPixels and save to a file in PPM format.
*
* - filename: file path to save to, without extension
* - width: screen width in pixels
* - height: screen height in pixels
* - pixels: intermediate buffer to avoid repeated mallocs across multiple calls.
* Contents of this buffer do not matter. May be NULL, in which case it is initialized.
* You must `free` it when you won't be calling this function anymore.
*/
static void screenshot_ppm(const char *filename, unsigned int width,
unsigned int height, GLubyte **pixels) {
size_t i, j, cur;
const size_t format_nchannels = 3;
FILE *f = fopen(filename, "w");
fprintf(f, "P3\n%d %d\n%d\n", width, height, 255);
*pixels = realloc(*pixels, format_nchannels * sizeof(GLubyte) * width * height);
glReadPixels(0, 0, width, height, GL_RGB, GL_UNSIGNED_BYTE, *pixels);
for (i = 0; i < height; i++) {
for (j = 0; j < width; j++) {
cur = format_nchannels * ((height - i - 1) * width + j);
fprintf(f, "%3d %3d %3d ", (*pixels)[cur], (*pixels)[cur + 1], (*pixels)[cur + 2]);
}
fprintf(f, "\n");
}
fclose(f);
}
#endif
#if LIBPNG
/* Adapted from https://github.com/cirosantilli/cpp-cheat/blob/19044698f91fefa9cb75328c44f7a487d336b541/png/open_manipulate_write.c */
static png_byte *png_bytes = NULL;
static png_byte **png_rows = NULL;
static void screenshot_png(const char *filename, unsigned int width, unsigned int height,
GLubyte **pixels, png_byte **png_bytes, png_byte ***png_rows) {
size_t i, nvals;
const size_t format_nchannels = 4;
FILE *f = fopen(filename, "wb");
nvals = format_nchannels * width * height;
*pixels = realloc(*pixels, nvals * sizeof(GLubyte));
*png_bytes = realloc(*png_bytes, nvals * sizeof(png_byte));
*png_rows = realloc(*png_rows, height * sizeof(png_byte*));
glReadPixels(0, 0, width, height, GL_RGBA, GL_UNSIGNED_BYTE, *pixels);
for (i = 0; i < nvals; i++)
(*png_bytes)[i] = (*pixels)[i];
for (i = 0; i < height; i++)
(*png_rows)[height - i - 1] = &(*png_bytes)[i * width * format_nchannels];
png_structp png = png_create_write_struct(PNG_LIBPNG_VER_STRING, NULL, NULL, NULL);
if (!png) abort();
png_infop info = png_create_info_struct(png);
if (!info) abort();
if (setjmp(png_jmpbuf(png))) abort();
png_init_io(png, f);
png_set_IHDR(
png,
info,
width,
height,
8,
PNG_COLOR_TYPE_RGBA,
PNG_INTERLACE_NONE,
PNG_COMPRESSION_TYPE_DEFAULT,
PNG_FILTER_TYPE_DEFAULT
);
png_write_info(png, info);
png_write_image(png, *png_rows);
png_write_end(png, NULL);
png_destroy_write_struct(&png, &info);
fclose(f);
}
#endif
#if FFMPEG
/* Adapted from: https://github.com/cirosantilli/cpp-cheat/blob/19044698f91fefa9cb75328c44f7a487d336b541/ffmpeg/encode.c */
static AVCodecContext *c = NULL;
static AVFrame *frame;
static AVPacket pkt;
static FILE *file;
static struct SwsContext *sws_context = NULL;
static uint8_t *rgb = NULL;
static void ffmpeg_encoder_set_frame_yuv_from_rgb(uint8_t *rgb) {
const int in_linesize[1] = { 4 * c->width };
sws_context = sws_getCachedContext(sws_context,
c->width, c->height, AV_PIX_FMT_RGB32,
c->width, c->height, AV_PIX_FMT_YUV420P,
0, NULL, NULL, NULL);
sws_scale(sws_context, (const uint8_t * const *)&rgb, in_linesize, 0,
c->height, frame->data, frame->linesize);
}
void ffmpeg_encoder_start(const char *filename, int codec_id, int fps, int width, int height) {
AVCodec *codec;
int ret;
avcodec_register_all();
codec = avcodec_find_encoder(codec_id);
if (!codec) {
fprintf(stderr, "Codec not found\n");
exit(1);
}
c = avcodec_alloc_context3(codec);
if (!c) {
fprintf(stderr, "Could not allocate video codec context\n");
exit(1);
}
c->bit_rate = 400000;
c->width = width;
c->height = height;
c->time_base.num = 1;
c->time_base.den = fps;
c->gop_size = 10;
c->max_b_frames = 1;
c->pix_fmt = AV_PIX_FMT_YUV420P;
if (codec_id == AV_CODEC_ID_H264)
av_opt_set(c->priv_data, "preset", "slow", 0);
if (avcodec_open2(c, codec, NULL) < 0) {
fprintf(stderr, "Could not open codec\n");
exit(1);
}
file = fopen(filename, "wb");
if (!file) {
fprintf(stderr, "Could not open %s\n", filename);
exit(1);
}
frame = av_frame_alloc();
if (!frame) {
fprintf(stderr, "Could not allocate video frame\n");
exit(1);
}
frame->format = c->pix_fmt;
frame->width = c->width;
frame->height = c->height;
ret = av_image_alloc(frame->data, frame->linesize, c->width, c->height, c->pix_fmt, 32);
if (ret < 0) {
fprintf(stderr, "Could not allocate raw picture buffer\n");
exit(1);
}
}
void ffmpeg_encoder_finish(void) {
uint8_t endcode[] = { 0, 0, 1, 0xb7 };
int got_output, ret;
do {
fflush(stdout);
ret = avcodec_encode_video2(c, &pkt, NULL, &got_output);
if (ret < 0) {
fprintf(stderr, "Error encoding frame\n");
exit(1);
}
if (got_output) {
fwrite(pkt.data, 1, pkt.size, file);
av_packet_unref(&pkt);
}
} while (got_output);
fwrite(endcode, 1, sizeof(endcode), file);
fclose(file);
avcodec_close(c);
av_free(c);
av_freep(&frame->data[0]);
av_frame_free(&frame);
}
void ffmpeg_encoder_encode_frame(uint8_t *rgb) {
int ret, got_output;
ffmpeg_encoder_set_frame_yuv_from_rgb(rgb);
av_init_packet(&pkt);
pkt.data = NULL;
pkt.size = 0;
ret = avcodec_encode_video2(c, &pkt, frame, &got_output);
if (ret < 0) {
fprintf(stderr, "Error encoding frame\n");
exit(1);
}
if (got_output) {
fwrite(pkt.data, 1, pkt.size, file);
av_packet_unref(&pkt);
}
}
void ffmpeg_encoder_glread_rgb(uint8_t **rgb, GLubyte **pixels, unsigned int width, unsigned int height) {
size_t i, j, k, cur_gl, cur_rgb, nvals;
const size_t format_nchannels = 4;
nvals = format_nchannels * width * height;
*pixels = realloc(*pixels, nvals * sizeof(GLubyte));
*rgb = realloc(*rgb, nvals * sizeof(uint8_t));
/* Get RGBA to align to 32 bits instead of just 24 for RGB. May be faster for FFmpeg. */
glReadPixels(0, 0, width, height, GL_RGBA, GL_UNSIGNED_BYTE, *pixels);
for (i = 0; i < height; i++) {
for (j = 0; j < width; j++) {
cur_gl = format_nchannels * (width * (height - i - 1) + j);
cur_rgb = format_nchannels * (width * i + j);
for (k = 0; k < format_nchannels; k++)
(*rgb)[cur_rgb + k] = (*pixels)[cur_gl + k];
}
}
}
#endif
static void model_init(void) {
angle = 0;
delta_angle = 1;
}
static int model_update(void) {
angle += delta_angle;
return 0;
}
static int model_finished(void) {
return nframes >= max_nframes;
}
static void init(void) {
int glget;
if (offscreen) {
/* Framebuffer */
glGenFramebuffers(1, &fbo);
glBindFramebuffer(GL_FRAMEBUFFER, fbo);
/* Color renderbuffer. */
glGenRenderbuffers(1, &rbo_color);
glBindRenderbuffer(GL_RENDERBUFFER, rbo_color);
/* Storage must be one of: */
/* GL_RGBA4, GL_RGB565, GL_RGB5_A1, GL_DEPTH_COMPONENT16, GL_STENCIL_INDEX8. */
glRenderbufferStorage(GL_RENDERBUFFER, GL_RGB565, width, height);
glFramebufferRenderbuffer(GL_DRAW_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_RENDERBUFFER, rbo_color);
/* Depth renderbuffer. */
glGenRenderbuffers(1, &rbo_depth);
glBindRenderbuffer(GL_RENDERBUFFER, rbo_depth);
glRenderbufferStorage(GL_RENDERBUFFER, GL_DEPTH_COMPONENT16, width, height);
glFramebufferRenderbuffer(GL_DRAW_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_RENDERBUFFER, rbo_depth);
glReadBuffer(GL_COLOR_ATTACHMENT0);
/* Sanity check. */
assert(glCheckFramebufferStatus(GL_FRAMEBUFFER));
glGetIntegerv(GL_MAX_RENDERBUFFER_SIZE, &glget);
assert(width < (unsigned int)glget);
assert(height < (unsigned int)glget);
} else {
glReadBuffer(GL_BACK);
}
glClearColor(0.0, 0.0, 0.0, 0.0);
glEnable(GL_DEPTH_TEST);
glPixelStorei(GL_PACK_ALIGNMENT, 1);
glViewport(0, 0, width, height);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glMatrixMode(GL_MODELVIEW);
time0 = glutGet(GLUT_ELAPSED_TIME);
model_init();
#if FFMPEG
ffmpeg_encoder_start("tmp.mpg", AV_CODEC_ID_MPEG1VIDEO, 25, width, height);
#endif
}
static void deinit(void) {
printf("FPS = %f\n", 1000.0 * nframes / (double)(glutGet(GLUT_ELAPSED_TIME) - time0));
free(pixels);
#if LIBPNG
if (output_formats & LIBPNG_BIT) {
free(png_bytes);
free(png_rows);
}
#endif
#if FFMPEG
if (output_formats & FFMPEG_BIT) {
ffmpeg_encoder_finish();
free(rgb);
}
#endif
if (offscreen) {
glDeleteFramebuffers(1, &fbo);
glDeleteRenderbuffers(1, &rbo_color);
glDeleteRenderbuffers(1, &rbo_depth);
}
}
static void draw_scene(void) {
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_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) {
char filename[SCREENSHOT_MAX_FILENAME];
draw_scene();
if (offscreen) {
glFlush();
} else {
glutSwapBuffers();
}
#if PPM
if (output_formats & PPM_BIT) {
snprintf(filename, SCREENSHOT_MAX_FILENAME, "tmp.%d.ppm", nframes);
screenshot_ppm(filename, width, height, &pixels);
}
#endif
#if LIBPNG
if (output_formats & LIBPNG_BIT) {
snprintf(filename, SCREENSHOT_MAX_FILENAME, "tmp.%d.png", nframes);
screenshot_png(filename, width, height, &pixels, &png_bytes, &png_rows);
}
#endif
# if FFMPEG
if (output_formats & FFMPEG_BIT) {
frame->pts = nframes;
ffmpeg_encoder_glread_rgb(&rgb, &pixels, width, height);
ffmpeg_encoder_encode_frame(rgb);
}
#endif
nframes++;
if (model_finished())
exit(EXIT_SUCCESS);
}
static void idle(void) {
while (model_update());
glutPostRedisplay();
}
int main(int argc, char **argv) {
int arg;
GLint glut_display;
/* CLI args. */
glutInit(&argc, argv);
arg = 1;
if (argc > arg) {
offscreen = (argv[arg][0] == '1');
} else {
offscreen = 1;
}
arg++;
if (argc > arg) {
max_nframes = strtoumax(argv[arg], NULL, 10);
}
arg++;
if (argc > arg) {
width = strtoumax(argv[arg], NULL, 10);
}
arg++;
if (argc > arg) {
height = strtoumax(argv[arg], NULL, 10);
}
arg++;
if (argc > arg) {
output_formats = strtoumax(argv[arg], NULL, 10);
}
/* Work. */
if (offscreen) {
/* TODO: if we use anything smaller than the window, it only renders a smaller version of things. */
/*glutInitWindowSize(50, 50);*/
glutInitWindowSize(width, height);
glut_display = GLUT_SINGLE;
} else {
glutInitWindowSize(width, height);
glutInitWindowPosition(100, 100);
glut_display = GLUT_DOUBLE;
}
glutInitDisplayMode(glut_display | GLUT_RGBA | GLUT_DEPTH);
glutCreateWindow(argv[0]);
if (offscreen) {
/* TODO: if we hide the window the program blocks. */
/*glutHideWindow();*/
}
init();
glutDisplayFunc(display);
glutIdleFunc(idle);
atexit(deinit);
glutMainLoop();
return EXIT_SUCCESS;
}
“屏幕外”运行10帧(主要是TODO,有效,但没有优势),尺寸为200 x 100,所有输出格式:
./offscreen 1 10 200 100 7
CLI格式为:
./offscreen [offscreen [nframes [width [height [output_formats]]]]]
输出格式是一个位掩码:
ppm >> 0 | png >> 1 | mpeg >> 2
在屏幕上运行(也不限制我的FPS):
以Ubuntu 15.10、OpenGL 4.4.0、NVIDIA 352.63、联想Thinkpad T430为基准
同样在ubuntu 18.04、OpenGL 4.6.0、NVIDIA 390.77、联想Thinkpad P51上进行了测试
TODO:找到一种在没有GUI(例如X11)的机器上执行此操作的方法。OpenGL似乎不是为屏幕外渲染而设计的,将像素读回GPU是在与窗口系统(例如)的接口上实现的。见:
TODO:使用1x1窗口,使其不可调整大小,并将其隐藏以使其更加健壮。如果执行上述任一操作,渲染将失败,请参见代码注释。看起来,但是。在任何情况下,这些都无关紧要,因为我的FPS不受屏幕刷新频率的限制,即使屏幕外
处于关闭状态
除PBO之外的其他选项
- 渲染到backbuffer(默认渲染位置)
- 渲染到纹理
- 渲染到
对象(PBO)像素缓冲区
Framebuffer
和Pixelbuffer
优于backbuffer和纹理,因为它们是为将数据读回CPU而制作的,而backbuffer和纹理则是为了留在GPU上并显示在屏幕上
PBO用于异步传输,因此我认为我们不需要它,请参见:
也许屏幕外的Mesa值得一看:
Vulkan
Vulkan的设计似乎比OpenGL更好地支持屏幕外渲染
这在NVIDIA概述中提到:
这是一个我刚刚设法在本地运行的可运行示例:
安装驱动程序后,我可以执行以下操作:
git clone https://github.com/SaschaWillems/Vulkan
cd Vulkan
b9f0ac91d2adccc3055a904d3a8f6553b10ff6cd
python download_assets.py
mkdir build
cd build
cmake ..
make -j`nproc`
cd bin
./renderheadless
这会立即生成图像headless.ppm
,而无需打开任何窗口:
我还设法运行了这个程序,这进一步表明它确实不需要屏幕
可能感兴趣的其他示例:
- 启动一个GUI,你可以点击一个按钮拍摄屏幕截图,它会保存到“屏幕截图”
- 渲染图像两次以创建反射效果
git clone https://github.com/apitrace/apitrace
cd apitrace
git checkout 7.0
mkdir build
cd build
cmake ..
make
# Creates opengl_executable.out.trace
./apitrace trace /path/to/opengl_executable.out
./apitrace dump-images opengl_executable.out.trace
也可在Ubuntu 18.10上使用:
sudo apt-get install apitrace
您现在有一组名为的屏幕截图:
animation.out.<n>.png
另见:
- 将图像转换为GIF:
- 图像到视频:
- 演示:
- 资料来源:
sudo apt-get install apitrace
animation.out.<n>.png
apitrace dump-images -o - application.trace \ | ffmpeg -r 30 -f image2pipe -vcodec ppm -i pipe: -vcodec mpeg4 -y output.mp4