unsigned int swidth = getMainScreen()->getWidth();
unsigned int sheight = getMainScreen()->getHeight();
std::vector< unsigned char > pixeldata;
pixeldata.resize( swidth * sheight * 3 );
// Clear the pixeldata variable
memset(&pixeldata.front(), 0, swidth * sheight * 3);
glReadPixels(0, 0, swidth, sheight, GL_RGB, GL_BYTE, &pixeldata.front());
// Used for debugging purposes
for (int i = 0; i < pixeldata.size(); ++i) {
std::cout << pixeldata;
}
std::cout << "\n\n";
SDL_Surface* image = SDL_CreateRGBSurfaceFrom(&pixeldata.front(), swidth, sheight, 24, 0,
// I'm a bit lost with the masks - hope this will work!
255U << (16),
255 << (8),
255 << (0),
0 /* no alpha! */);
// Used for debugging purposes
if ( image == NULL ) {
std::cout << "SDL_Surface creation failed!\n\n";
}
SDL_SaveBMP(image, filename.c_str());
Bitmap file saving problem.
Author
Hi all,
I have the following code:
By the looks of the std::cout output the glReadPixels() function is doing its job. The SDL_Surface also appears to be being created correctly as the if statement isn't entered. The problem is that the BMP file that is saved isn't readable by any image editing application and it's also 54 bytes which can't be right as the stdout.txt file output by the std::cout calls is well over 1.5 megs.
Any help in solving this problem is appreciated.
Thanks and take care.
Here is some code.
GLubyte *data = new GLubyte[pPreferences->Screen_W * pPreferences->Screen_H * 3]; // read gl screen glReadPixels( 0, 0, pPreferences->Screen_W, pPreferences->Screen_H, GL_RGB, GL_UNSIGNED_BYTE, (GLvoid *)data ); // create SDL surface SDL_Surface *temp = SDL_CreateRGBSurface( SDL_SWSURFACE, pPreferences->Screen_W, pPreferences->Screen_H, 32, 0x000000ff, 0x0000ff00, 0x00ff0000, 0xff000000 ); SDL_LockSurface( temp ); Uint32 *pdata = (Uint32 *)temp->pixels; // copy into SDL surface for( int y = temp->h - 1, y2 = 0; y >= 0 && y2 < pPreferences->Screen_H; --y, ++y2 ) { for( int x = temp->w -1; x >= 0; --x ) { pdata[y * temp->pitch/4 + x] = SDL_MapRGBA( temp->format, data[ y2 * pPreferences->Screen_W * 3 + x * 3 + 0 ], data[ y2 * pPreferences->Screen_W * 3 + x * 3 + 1 ], data[ y2 * pPreferences->Screen_W * 3 + x * 3 + 2 ], 255 ); } } SDL_UnlockSurface( temp ); // save the surface SDL_SaveBMP( temp, filename ); // delete screen data SDL_FreeSurface( temp ); delete[] data;
Author
Thanks a lot for that Boder.
I'll take a look at that code and import it into my project, I'll let you know how it goes.
I'll take a look at that code and import it into my project, I'll let you know how it goes.
Author
It works - sort of.
I'm getting the following output:
http://www.arronbailiss.co.uk/junk/fife/screenshot1.jpg
But it should look like this:
http://www.arronbailiss.co.uk/junk/fife/screenshot2.jpg
Here's my code:
Thanks
I'm getting the following output:
http://www.arronbailiss.co.uk/junk/fife/screenshot1.jpg
But it should look like this:
http://www.arronbailiss.co.uk/junk/fife/screenshot2.jpg
Here's my code:
GLubyte *data = new GLubyte[swidth * sheight * 3];// Read the screen and store it into "data"glReadPixels( 0, 0, swidth, sheight, GL_RGB, GL_UNSIGNED_BYTE, (GLvoid *)data );// Create the temporary SDL surfaceSDL_Surface *temp = SDL_CreateRGBSurface( SDL_SWSURFACE, swidth, sheight, 24, // Bit depth 255U << (16), // Red channel 255 << (8), // Green channel 255 << (0), // Blue channel 0 /* no alpha! */ );SDL_LockSurface( temp );Uint32 *pdata = (Uint32 *)temp->pixels;// copy into SDL surfacefor( int y = temp->h - 1, y2 = 0; y >= 0 && y2 < sheight; --y, ++y2 ){ for( int x = temp->w -1; x >= 0; --x ) { pdata[y * temp->pitch/4 + x] = SDL_MapRGBA( temp->format, data[ y2 * swidth * 3 + x * 3 + 0 ], data[ y2 * swidth * 3 + x * 3 + 1 ], data[ y2 * swidth * 3 + x * 3 + 2 ], 255 ); }}SDL_UnlockSurface( temp );// Save the screenshotSDL_SaveBMP( temp, filename.c_str() ); // Free up memorySDL_FreeSurface( temp );delete[] data;Thanks
Your alignment is probably messed up by casting to an array like
Uint32,
you should cast to a BYTE array
You might be able to read pixels right into the surface. Try this [smile]
Uint32,
you should cast to a BYTE array
You might be able to read pixels right into the surface. Try this [smile]
// Create the temporary SDL surfaceSDL_Surface *temp = SDL_CreateRGBSurface( SDL_SWSURFACE, swidth, sheight, 24, // Bit depth 255U << (16), // Red channel 255 << (8), // Green channel 255 << (0), // Blue channel 0 /* no alpha! */ );SDL_LockSurface( temp );// Read the screen and store it into "data"glReadPixels( 0, 0, swidth, sheight, GL_RGB, GL_UNSIGNED_BYTE, (GLvoid *)temp->pixels );SDL_UnlockSurface( temp );// Save the screenshotSDL_SaveBMP( temp, filename.c_str() ); // Free up memorySDL_FreeSurface( temp );
Stick with the vector (although make it a vector of GLubyte rather than of unsigned char) rather than doing the allocation yourself - you had a perfectly good idea there. Also, with the resize() call, you don't then need to memset: the vector will be implicitly filled with "default-constructed" GLubytes (i.e. with zero value):
That old C stuff is ugly anyway; in C++, prefer std::fill when you need to "memset".
Quote:
teh sgi docz0r (emphasis mine)
[std::vector::resize prototype:] void resize(n, t = T())
[semantics of a.resize(n, t):] ... [m]odifies the container so that it has exactly n elements, inserting elements at the end or erasing elements from the end if necessary. If any elements are inserted, they are copies of t.
That old C stuff is ugly anyway; in C++, prefer std::fill when you need to "memset".
Author
Alright now it's creating the full image, but the RGB channels are wrong and the image is upside-down.
I've fiddled with it a little and this is what I've achieved:
http://www.arronbailiss.co.uk/junk/fife/screenshot5.jpg
Here's the current code:
Does anyone have any idea what the problem is and am I defining the RGB channels correctly (255U << (16), 255 << (8) and 255 << (0))?
Thanks a lot for all of your help.
I've fiddled with it a little and this is what I've achieved:
http://www.arronbailiss.co.uk/junk/fife/screenshot5.jpg
Here's the current code:
unsigned int swidth = getMainScreen()->getWidth();unsigned int sheight = getMainScreen()->getHeight();std::vector< GLubyte > pixeldata;pixeldata.resize( swidth * sheight * 3 );SDL_Surface* image = SDL_CreateRGBSurface(SDL_SWSURFACE, swidth, sheight, 24,// I'm a bit lost with the masks - hope this will work! 255U << (16), 255 << (8), 255 << (0), 0 /* no alpha! */);SDL_LockSurface( image );glReadPixels(0, 0, swidth, sheight, GL_RGB, GL_UNSIGNED_BYTE, (GLvoid *)image->pixels);SDL_UnlockSurface( image ); SDL_SaveBMP(image, filename.c_str());SDL_FreeSurface( image );Does anyone have any idea what the problem is and am I defining the RGB channels correctly (255U << (16), 255 << (8) and 255 << (0))?
Thanks a lot for all of your help.
Author
Hi again all,
The screwed colours have been fixed by switching the B and R values around. I've tried to flip the image by copying the pixel data from "reversed_image" to "image" in reverse order but I'm receiving the compile error.
Current code:
The error is: pointer of type 'void *' used in arithmetic
Thanks again :-).
The screwed colours have been fixed by switching the B and R values around. I've tried to flip the image by copying the pixel data from "reversed_image" to "image" in reverse order but I'm receiving the compile error.
Current code:
void RenderBackendOpenGL::captureScreen(const std::string& filename) { unsigned int swidth = getMainScreen()->getWidth(); unsigned int sheight = getMainScreen()->getHeight(); unsigned char *pixels = malloc (swidth * sheight * 3); SDL_Surface* reversed_image = SDL_CreateRGBSurface(SDL_SWSURFACE, swidth, sheight, 24, 255U << (0), // Blue channel 255 << (8), // Green channel 255 << (16), // Red channel 0 /* no alpha! */); SDL_LockSurface( reversed_image ); // Read in the pixel data glReadPixels(0, 0, swidth, sheight, GL_RGB, GL_UNSIGNED_BYTE, pixels); SDL_UnlockSurface( reversed_image ); /* At this point the image has been reversed, so we need to re-reverse it so that it is the correct way around. We do this by copying the "image" pixels to another surface in reverse order */ SDL_Surface* image = SDL_CreateRGBSurface(SDL_SWSURFACE, swidth, sheight, 24, 255U << (0), // Blue channel 255 << (8), // Green channel 255 << (16), // Red channel 0 /* no alpha! */); // Copy the "reversed_image" memory to the "image" memory for (int i = 0; i < sheight; ++i) { memcpy(image->pixels + image->pitch*i, pixels + image->pitch*(sheight-i-1), swidth * 3); // This is where I'm getting the compile error. } // Save file SDL_SaveBMP(image, filename.c_str()); // Clear memory SDL_FreeSurface( reversed_image ); SDL_FreeSurface( image );}The error is: pointer of type 'void *' used in arithmetic
Thanks again :-).
Quote:Original post by Undeadlnsanity
Hi again all,
The screwed colours have been fixed by switching the B and R values around. I've tried to flip the image by copying the pixel data from "reversed_image" to "image" in reverse order but I'm receiving the compile error.
Don't do that. Instead, reverse the bounds of the loop that iterates over rows.
(The reason you need to do this is that the BMP format actually stores the row data bottom to top. Apparently, this was thought to be a pretty slick hack back when computers were really slow, because it reduced flicker when the image was being drawn and loaded at the same time and took a few refresh cycles to load. Or something like that, anyway.)
And like I said, please stick with the vector, and things like std::fill - or in this case, std::copy. You'll be thankful you did sooner or later.
Author
I don't quite understand your suggestion Zahlman. What do you mean by "reverse the bounds of the loop that iterates over rows"?
Thanks :-).
Thanks :-).
This topic is closed to new replies.
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