Surface

pygame里的Surface是用来表示图像的对象。Surface有一定的大小和像素格式。如果是8bit像素格式的Surface，它还会用一个调色板映射到24比特颜色。

调用pygame.Surface可以创建表示图像的新对象。Surface会整个全是黑的。唯一需要指定的参数是大小。如果不指定其他参数，Surface的像素格式会与display Surface的像素格式尽量一致。

像素格式可以通过指定像素深度或者已有的Surface来控制。flag标志位参数是其他一些Surface选项的集合，你可以指定如下的标志

• HWSURFACE, 在视频内存中创建图像
• SRCALPHA, 像素格式中会包含一个alpha通道

这些参数都仅仅是一个请求，在实际中可能并不能实现。

Advance users can combine a set of bitmasks with a depth value. The masks are a set of 4 integers representing which bits in a pixel will represent each color. Normal Surfaces should not require the masks argument.

Surfaces can have many extra attributes like alpha planes, colorkeys, source rectangle clipping. These functions mainly effect how the Surface is blitted to other Surfaces. The blit routines will attempt to use hardware acceleratio

• when possible, otherwise will use highly optimized software blitting methods.

There are three types of transparency supported in Pygame: colorkeys, surface alphas, and pixel alphas. Surface alphas can be mixed with colorkeys, but an image with per pixel alphas cannot use the other modes. Colorkey transparency makes a single color value transparent. Any pixels matching the colorkey will not be drawn. The surface alpha value is a single value that changes the transparency for the entire image. A surface alpha of 255 is opaque, and a value of 0 is completely transparent.

Per pixel alphas are different because they store a transparency value for every pixel. This allows for the most precise transparency effects, but it also the slowest. Per pixel alphas cannot be mixed with surface alpha and colorkeys.

There is support for pixel access for the Surfaces. Pixel access on hardware surfaces is slow and not recommended. Pixels can be accessed using the get_at() and set_at() functions. These methods are fine for simple access, but will be considerably slow when doing of pixel work with them. If you plan on doing a lot of pixel level work, it is recommended to use the pygame.surfarray module, which can treat the surfaces like large multidimensional arrays (and it's quite quick).

Any functions that directly access a surface's pixel data will need that surface to be lock()'ed. These functions can lock() and unlock() the surfaces themselves without assistance. But, if a function will be called many times, there will be a lot of overhead for multiple locking and unlocking of the surface. It is best to lock the surface manually before making the function call many times, and then unlocking when you are finished. All functions that need a locked surface will say so in their docs. Remember to leave the Surface locked only while necessary.

Surface pixels are stored internally as a single number that has all the colors encoded into it. Use the Surface.map_rgb - convert a color into a mapped color value and Surface.unmap_rgb - convert a mapped integer color value into a Color to convert between individual red, green, and blue values into a packed integer for that Surface.

Surfaces can also reference sections of other Surfaces. These are created with the Surface.subsurface - create a new surface that references its parent method. Any change to either Surface will effect the other.

Each Surface contains a clipping area. By default the clip area covers the entire Surface. If it is changed, all drawing operations will only effect the smaller area.