SDL_SaveBMP() problems
Author
I'm writing a software to visualize volume-data with SDL/OpenGL on linux, and I thought that it would be nice to have a function to take a screenshot of the window.
It happens that calling
SDL_SaveBMP(app_screen "screenshot.bmp")
where:
SDL_Surface *app_screen
is a valid (checked not NULL) pointer to the whole-screen surface, I always get a segmentation fault.
SDL version is 1.2.something (debian sid), Anyone experiencing this?
Marco
There could be a few problems.
1. The screen surface could be locked. Try unlocking it.
2. You don't have access to write the bitmap. (check permissions)
Try saving to "./screenshot.bmp" instead of "screenshot.bmp"
Try to see what it returns. SDL_SaveBMP() returns 0 if successful or -1 if there is an error. Hopefully you can get the result before it crashes. [Edit: If the image wasn't created then it probly didn't work.]
Personally I would add a time stamp or look up my OS's filesystem code and increment a number on the screenshot file name. ei. "screenshot#.bmp"
1. The screen surface could be locked. Try unlocking it.
2. You don't have access to write the bitmap. (check permissions)
Try saving to "./screenshot.bmp" instead of "screenshot.bmp"
Try to see what it returns. SDL_SaveBMP() returns 0 if successful or -1 if there is an error. Hopefully you can get the result before it crashes. [Edit: If the image wasn't created then it probly didn't work.]
if(SDL_SaveBMP(app_screen, "./screenshot.bmp") != 0){ std::cerr << "SDL_SaveBMP() Failed." << std::endl;}Personally I would add a time stamp or look up my OS's filesystem code and increment a number on the screenshot file name. ei. "screenshot#.bmp"
Author
first, thanks for your help :)
the actual code was like yours:
My output is only: "Fatal signal: Segmentation Fault (SDL Parachute Deployed)" I never get the return value, so I think that the segfault happens during the execution of SDL_SaveBMP()
When I will be proficient in gdb...
I tried locking first the surface, nothing.
I tried unlocking... the same.
Permissions are ok, an empty screen.bmp file is created.
:)
... i was thinking like you about the auto-incremented filename, actually something more than a counter... maybe the coords of the plane showed within the volume or something else...
Thanks Anyway :)
Marco
the actual code was like yours:
.../* grabbing the s key */if (keysym.sym == SDLK_s) { if (SDL_SaveBMP(app_screen, "screen.bmp") != 0) { fprintf(stderr, "--> Failed to take screenshot\n"); } else { printf("--> Screenshot saved to screen.bmp\n"); } }...My output is only: "Fatal signal: Segmentation Fault (SDL Parachute Deployed)" I never get the return value, so I think that the segfault happens during the execution of SDL_SaveBMP()
When I will be proficient in gdb...
I tried locking first the surface, nothing.
I tried unlocking... the same.
Permissions are ok, an empty screen.bmp file is created.
:)
... i was thinking like you about the auto-incremented filename, actually something more than a counter... maybe the coords of the plane showed within the volume or something else...
Thanks Anyway :)
Marco
If you're using OpenGL you can't use SDL_SaveBMP to make a screenshot. In this case you have to read the framebuffer yourself and write the contents to a file.
Here's an example I found on this board
Here's an example I found on this board
void Screendump(char *destFile, short W, short H) { FILE *out = fopen(destFile, "w"); char pixel_data[3*W*H]; short TGAhead[] = {0, 2, 0, 0, 0, 0, W, H, 24}; glReadBuffer(GL_FRONT); glReadPixels(0, 0, W, H, GL_BGR, GL_UNSIGNED_BYTE, pixel_data); fwrite(&TGAhead, sizeof(TGAhead), 1, out); fwrite(pixel_data, 3*W*H, 1, out); fclose(out); }/* ______________________________________________________________ creates a 24-bit uncompressed true color tga-file, width W and height H. for a complete description of tga go to www.wotsit.org. if you use a doublebuffered configuration, be sure to swap buffers before you call the screendump function.*/
Author
It seems so :)
I just wrongly assumed that the screen was just another SDL_Surface while initializing SDL to provide the OpenGL context.
Thank you very much indeed.
I just wrongly assumed that the screen was just another SDL_Surface while initializing SDL to provide the OpenGL context.
Thank you very much indeed.
This topic is closed to new replies.
Advertisement
Popular Topics
Advertisement
