- How can I link/use Gfxlib?
- What about the fbgfx.bi header file?
- How are Get/Put arrays managed?
- Why is Bsave/Bload crashing?
- How can I get the red, green, blue, or alpha component of a colour?
- How can I make the 'x' button in the window header close my application?
- Can't run programs using Screen 13 or 14 in fullscreen !
- Why does Imagecreate return a NULL pointer?
- Why does a low resolution graphics screen get bigger when I maximize the window?

Gfxlib is "built in" into the language, it is not necessary to include any .bi file or to link any library explicitly. FreeBASIC detects you want to use Gfxlib when you use the Screen (Graphics) or ScreenRes statements. So to use Gfxlib, just start a graphics screen mode and use the graphics commands.

The fbgfx.bi header file is available for inclusion by your program, and contains constant and type definitions that may be helpful to the programmer when using Gfxlib. You do not have to explicitly include this file to use Gfxlib however; the header is only available as an aid. It contains the constants for the mode flags that can be passed to Screen (Graphics) and ScreenRes, and also definitions of Keyboard scancodes and the fb.Image buffer structure.

In FreeBASIC, images can be used as arrays (as in QB) or as pointers. Either way, the image data is contained in one continuous chunk. The chunk consists of an header followed by the image data. The header can be of two types (old-style and new-style) and determines the format of the following image data, for details see GfxInternalFormats .

Bsave/Bload can only be used to load and save graphics screens in FreeBASIC. It can't be used to save a text mode screen. To load and save an array check this snippet using file Get/Put .

Each byte in a color attribute corresponds with the red, green, blue, and alpha components. The following example shows how to extract the component values from a 16, 24, or 32 bit color attribute.

In windowed graphics mode you can test for the press of the window's X (close) button with Inkey, checking for the value Chr( 255 ) + "k" (which is also the code returned for Alt+F4). This applies to Win32 and Linux, in DOS there is no "X" button.

Here is a small example:

Modern hardware and display systems often do not expose old low-resolution modes such as 320x200 directly. On current backends this is less of a problem than it used to be: several drivers can keep the program's logical framebuffer at the requested size while presenting it centered and integer-scaled on a larger display or in a maximized window.

This means Screen 13 can still behave like a 320x200 screen to the program, while the driver presents it at a larger clean scale when possible. If a backend cannot provide the requested mode or an integer-scaled presentation, use ScreenList or a safer fallback resolution such as 640x480.

ImageCreate needs to create an image buffer that fits the current screen's pixel format, and it cannot do so if there is no screen mode setup yet, so it returns NULL, very likely resulting in a NULL pointer access later on that crashes the program.

This is known to happen when Imagecreate is called before the graphics library was initialized with a call to Screen (Graphics) or ScreenRes, as may happen when Imagecreate is called in a global constructor that is invoked before the Screen or Screenres call in the main part of the program. In such a case it is necessary to move the screen initialization into a constructor too, and have it execute before the image-creating constructors.

Several GfxLib backends use centered integer scaling when the visible window or display is larger than the program's framebuffer. For example, a 320x200 screen on a 1920x1080 display can be shown as a centered 1600x1000 image at 5x scale. The program still sees a 320x200 framebuffer, and mouse/touch coordinates are mapped back to that logical size.

Integer scaling is used because it keeps old pixel-art and QB-style graphics sharp. It also avoids lying to the program about the screen size. If you are building the runtime yourself and really want low-resolution screens to stay physically small even in a larger window or display area, build gfxlib2 with -DGFXLIB_NEVERSCALE.