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fixed sf::Image::create

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Discussion thread: http://en.sfml-dev.org/forums/index.php?topic=20875.0
Basically, the issue with sf::Image::create was, that it would either
occupy space, it doesn't need, because std::vector::resize doesn't
actually shrink the vector, or reallocate in an inefficient way by
needlessly copying the whole old image over. Neither did it grant strong
exception safety guarantee because it changed the non-throwing members
(m_size) prior to doing the critical stuff (reallocating) which may
throw. Changing the order and using a temporary
(create-temporary-and-swap idiom; see http://www.gotw.ca/gotw/059.htm)
fixes both of these problems.
This commit is contained in:
Fytch 2016-11-11 11:52:20 +01:00 committed by Lukas Dürrenberger
parent 8c7c48481b
commit c678cae498
1 changed files with 26 additions and 18 deletions
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42
src/SFML/Graphics/Image.cpp
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@ -66,16 +66,12 @@ void Image::create(unsigned int width, unsigned int height, const Color& color)
{ {
if (width && height) if (width && height)
{ {
// Assign the new size // Create a new pixel buffer first for exception safety's sake
m_size.x = width; std::vector<Uint8> newPixels(width * height * 4);
m_size.y = height;
// Resize the pixel buffer
m_pixels.resize(width * height * 4);
// Fill it with the specified color // Fill it with the specified color
Uint8* ptr = &m_pixels[0]; Uint8* ptr = &newPixels[0];
Uint8* end = ptr + m_pixels.size(); Uint8* end = ptr + newPixels.size();
while (ptr < end) while (ptr < end)
{ {
*ptr++ = color.r; *ptr++ = color.r;
@ -83,13 +79,22 @@ void Image::create(unsigned int width, unsigned int height, const Color& color)
*ptr++ = color.b; *ptr++ = color.b;
*ptr++ = color.a; *ptr++ = color.a;
} }
// Commit the new pixel buffer
m_pixels.swap(newPixels);
// Assign the new size
m_size.x = width;
m_size.y = height;
} }
else else
{ {
// Create an empty image // Dump the pixel buffer
std::vector<Uint8>().swap(m_pixels);
// Assign the new size
m_size.x = 0; m_size.x = 0;
m_size.y = 0; m_size.y = 0;
m_pixels.clear();
} }
} }
@ -99,21 +104,24 @@ void Image::create(unsigned int width, unsigned int height, const Uint8* pixels)
{ {
if (pixels && width && height) if (pixels && width && height)
{ {
// Create a new pixel buffer first for exception safety's sake
std::vector<Uint8> newPixels(pixels, pixels + width * height * 4);
// Commit the new pixel buffer
m_pixels.swap(newPixels);
// Assign the new size // Assign the new size
m_size.x = width; m_size.x = width;
m_size.y = height; m_size.y = height;
// Copy the pixels
std::size_t size = width * height * 4;
m_pixels.resize(size);
std::memcpy(&m_pixels[0], pixels, size); // faster than vector::assign
} }
else else
{ {
// Create an empty image // Dump the pixel buffer
std::vector<Uint8>().swap(m_pixels);
// Assign the new size
m_size.x = 0; m_size.x = 0;
m_size.y = 0; m_size.y = 0;
m_pixels.clear();
} }
} }