Screen (Graphics)

FreeBASIC

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Screen (Graphics)

Initializes a graphics mode using QB-like mode numbers

Syntax

-lang fb|fblite dialects:Screen mode [, [ depth ] [, [ num_pages ] [, [ flags ] [, [ refresh_rate ]]]]] Screen , [ active_page ] [, [ visible_page ]]-lang qb dialect:Screen [ mode ] [, [ colormode ] [, [ active_page ] [, [ visible_page ]]]]

Parameters

mode

is a QB style graphics screen mode number (see below). If mode is 0, then any currently set graphics mode is closed, and all functions resume their normal console-mode functionality. See below for available modes.

depth

is the color depth in bits per pixel. This only has an effect for modes 14 and higher. Values of 8, 16 and 32 are allowed. 15 and 24 are also allowed as aliases for 16 and 32, respectively. If omitted, it defaults to 8.

num_pages

is the number of video pages you want, see below. If omitted, it defaults to 1.

flags

Are used to select several things as graphics driver, fullscreen mode. There are constants predefined in the fbgfx.bi file ready to use. See the page ScreenRes for available flags.

refresh_rate

requests a refresh rate. If it is not available in the present card or the parameter is omitted, FreeBASIC chooses the rate automatically.

active_page

Used to set the active page, where printing/drawing commands take effect

visible_page

Used to set the visible page, which is shown to the user

colormode

Unused - allowed for compatibility with the QB syntax

Description

Screen tells the compiler to link the GfxLib and initializes a QB-only, QB-on-GUI or OpenGL graphics mode, depending on the flags setting.

In QB-only modes a dumb window or fullscreen resolution is set, one or more buffers in standard memory are created, console commands are redirected to their graphic versions, a default palette is set and an automatic screen refresh thread is started. QB-like graphics and console statements can be used.

In QB-on-GUI modes one or more buffers in standard memory are created, console commands are redirected to their graphic versions and a default palette is set. QB-like graphics and console statements can be used. It is up to the user to create a window and to refresh it with the contents of the graphics buffers.

In OpenGL modes a dumb window or fullscreen resolution is set, one or more buffers in standard memory are created, and the OS's OpenGL library is initialized. From here only OpenGL commands can be used; QB-like and console commands are forbidden. This allows to initialize OpenGL in a portable way; you can then also use ScreenControl to properly customize the GL pixel format to be used before Screen is called or to retrieve the list of supported OpenGL extensions after a mode has been set, and ScreenGLProc to obtain extension function pointers.

Any buffer that is created in standard memory uses one of three supported internal pixel formats, depending on the desired color depth; see Internal pixel formats for details.

If Screen fails to set the required mode, an "Illegal function call" error is issued and the screen pointer is set to 0. Thus Screen failures can be detected using standard On Error processing or retrieving the screen pointer with ScreenPtr.

Before setting a fullscreen mode the program should check if that mode is available in the graphics card using ScreenList.

mode details
Available modes list:
QB compatibility modes:

Mode nr	Resolution	Emulation	Text	char size	colors on screen
1	320x200	CGA	40X25	8x8	16 background, 1 of four sets foreground
2	640x200	CGA	80x25	8x8	16 colors to 2 attributes
7	320x200	EGA	40x25	8x8	16 colors to 16 attributes
8	640x200	EGA	80x25	8x8	16 colors to 16 attributes
9	640x350	EGA	80x25 0r 80x43	8x14 or 8x8	16 colors to 16 attributes
11	640x480	VGA	80x30 or 80x60	8x16 or 8x8	256K colors to 2 attributes
12	640x480	VGA	80x30 or 80x60	8x16 or 8x8	256K colors to 16 attributes
13	320x200	MCGA	40X25	8X8	256K colors to 256 attributes

New FreeBASIC modes:

Mode nr	Resolution	Emulation	Text	char size	colors on screen
14	320x240		40x30	8x8	256K colors to 256 attributes or direct color
15	400x300		50x37	8x8	256K colors to 256 attributes or direct color
16	512x384		64x24 or 64x48	8x16 or 8x8	256K colors to 256 attributes or direct color
17	640x400		80x25 or 80x50	8x16 or 8x8	256K colors to 256 attributes or direct color
18	640x480		80x30 or 80x60	8x16 or 8x8	256K colors to 256 attributes or direct color
19	800x600		100x37 or 100x75	8x16 or 8x8	256K colors to 256 attributes or direct color
20	1024x768		128x48 or 128x96	8x16 or 8x8	256K colors to 256 attributes or direct color
21	1280x1024		160x64 or 160x128	8x16 or 8x8	256K colors to 256 attributes or direct color

depth details
For modes 14 and up, the depth parameter changes the color depth to the specified new one; if depth is not specified, these modes run in 8bpp. For modes 13 and below, depth has no effect.

num_pages details
You can request any number of pages for any video mode; if you omit the parameter, only the visible page (number 0) will be available. A page is either the visible screen or an offscreen buffer, you can show a page while working on another one; see the ScreenSet statement for details. All pages are created in standard memory, the video card memory is never used for video buffering.

flags details:
(documented at the page ScreenRes)

Other details
While in windowed mode, clicking on the window close button will add a keypress of (Chr(255) & "k") to the Inkey buffer. Clicking on the Maximize window button will switch to fullscreen mode if possible. A successful Screen call sets currently visible and working pages both to page number 0, resets the palette to the specified mode one (see Default palettes), resets the clipping region to the size of the screen, disables custom coordinates mappings, moves the graphics cursor to the center of the screen, moves the text cursor to the top-left corner of the screen and sets foreground and background colors to bright white and black respectively.

Example

' Sets screen mode 13 (320*200, 8bpp) Screen 13 Print "Screen mode 13 set" Sleep

#include "fbgfx.bi" #if __FB_LANG__ = "fb" Using FB '' Screen mode flags are in the FB namespace in lang FB #endif ' Sets screen mode 18 (640*480) with 32bpp color depth and 4 pages, in windowed mode; switching disabled Screen 18, 32, 4, (GFX_WINDOWED Or GFX_NO_SWITCH) ' Check to make sure Screen was opened successfully If ScreenPtr = 0 Then Print "Error setting video mode!" End End If Print "Successfully set video mode" Sleep

Platform Differences

In DOS, Windowing and OpenGL related switches are not available, and other issues, see GfxLib overview

Dialect Differences

In the -lang fb and -lang fblite dialects, the usage is:

Screen mode [, [depth] [, [num_pages] [, [flags] [, [refresh_rate]]]]]

or:

Screen , [active_page] [, [visible_page]]]

In the -lang qb dialect, the usage is:

Screen [mode] [, [colormode] [, [active_page] [, [visible_page]]]]

Differences from QB

None in the -lang qb dialect.
In QB the syntax was Screen mode,colormode,active_page,visible_page. Of those parameters FreeBASIC supports only mode and redefines the rest. The use of Screen , , apage,vpage to swap screen pages is only available in the -lang qb dialect.
ScreenSet should be used in the -lang fb and -lang fblite dialects.