FreeBASIC gfx 基本 graphics 绘图
一、旧故事
DOS时代PC技术将各类硬插卡限制在 640K到1MB的空间范围内，BIOS负责在相关位置写读测试卡的存在，那时期的Color Video在0xB800，Monochrome Video在0xB000，这是显卡的内存地址，字符方式下通常用2个byte共16位显示一个字符，首字节是ASCII值，另外一个字节(8BIT)为属性字节，高4位表示背景色、低4位表示前景色。因为用4位颜色表示，0xF种色彩就是16种颜色，编号 0 - 15。
QuickBASIC示例 - 白字蓝底：
Color 15, 1: Locate 12, 32: Print "Hello World!"
二、FreeBASIC进化
随着视窗的发展，一些复杂的内存管理交给了CPU处理，不再是原来与卡密切相关的固定显存地址，取而代之的是可大可小的窗口。FreeBASIC保留了原有的13种显示模式，同时增加到了21种，达到1280x1024, 160列x128行，256K颜色。
除此之外，继续演进，增加了screenres 指令，可以任意定义窗口尺寸，比如： screenres 1920, 1080, 32, 5, 0, 0 或简写为 screenres 1920, 1080, 32 ， 其它参数均为 default 值。它创建一个 1920x1080像素的屏幕(不是实际意义上的屏幕，但仍称其为screen，是个绘图用的surface而已)，用32位颜色，5个页面(一个活动可见页面，其它的在内存中不可见，考贝到可见页即可见)， 接着的0表示全屏或显示驱动的选择。由于相关定义变得复杂，此时编程需使用 gfxlib 支持。
三、屏幕变为窗口后的编程
1、示例一：屏幕变为窗口
screen 9是640x480标准模式。过去，设置完屏幕方式后即可print或line绘图; 现在，它是一个窗口，因此，可以设置它的标题 WindowTitle "FreeBASIC example program"，还可加一句非常简便的无限等待 sleep 语句，直到有按键动作时退出。
Locate 和 Line 都是传统 QBasic 使用的绘图语句。
'' examples/manual/gfx/windowtitle.bas
''
'' Example extracted from the FreeBASIC Manual
'' from topic 'WINDOWTITLE'
''
'' See Also: https://www.freebasic.net/wiki/wikka.php?wakka=KeyPgWindowtitle
'' --------
'' Modified: Mongnewer 9, March 2024
'Set screen mode
Screen 9
'Set the window title
WindowTitle "FreeBASIC example program"
Locate 12, 35: Print "Hello World!"
line (200, 100) - (440, 220), 4, b
Sleep
2、绘图锁定与缩放
在屏幕绘图前先 screenlock, 绘图后 screenunlock, 并通过 window 函数改变座标系而circle本身的参数则无需变化。屏幕上显示一个连续缩放的黄色填充的圆形，锁定的目的是绘图完成后一次性显示到屏幕上，避免了绘制过程的拖慢效果。
'' examples/manual/gfx/window2.bas
''
'' Example extracted from the FreeBASIC Manual
'' from topic 'WINDOW'
''
'' See Also: https://www.freebasic.net/wiki/wikka.php?wakka=KeyPgWindow
'' --------
'' The program shows how changing the view coordinates mapping for the current viewport changes the size of a figure drawn on the screen.
'' The effect is one of zooming in and out:
'' - As the viewport coordinates get smaller, the figure appears larger on the screen, until parts of it are finally clipped,
'' because they lie outside the window.
'' - As the viewport coordinates get larger, the figure appears smaller on the screen.
'' ---------------------------------
'' Modified: Mongnewer 9, March 2024
Declare Sub Zoom (ByVal X As Integer)
Dim As Integer X = 500, Xdelta = 50
Screen 12
Do
Do While X < 525 And X > 50
X += Xdelta '' Change window size.
Zoom(X)
If Inkey <> "" Then Exit Do, Do '' Stop if key pressed.
Sleep 100
Loop
X -= Xdelta
Xdelta *= -1 '' Reverse size change.
Loop
Sub Zoom (ByVal X As Integer)
Window (-X,-X)-(X,X) '' Define new window.
ScreenLock
Cls
Circle (0,0), 60, 14, , , 0.7, F '' Draw ellipse with x-radius 60.
ScreenUnlock
End Sub
3 、view and window, draw string
view 是在screen窗口中创建视图区，而window 语句是视图区的新座标系、不带参数时取消所建立的座标系，Draw string 与 print 类似但又不同， 它不同按行显示字符串，是按 x, y 位置绘制字符串。
'' examples/manual/gfx/window.bas
''
'' Example extracted from the FreeBASIC Manual
'' from topic 'WINDOW'
''
'' See Also: https://www.freebasic.net/wiki/wikka.php?wakka=KeyPgWindow
'' --------
Screen 13
'' define clipping area
View ( 10, 10 ) - ( 310, 150 ), 1, 15
'' set view coordinates
Window ( -1, -1 ) - ( 1, 1 )
'' Draw X axis
Line (-1,0)-(1,0),7
Draw String ( 0.8, -0.1 ), "X"
'' Draw Y axis
Line (0,-1)-(0,1),7
Draw String ( 0.1, 0.8 ), "Y"
Dim As Single x, y, s
'' compute step size (corresponds to a step of 1 pixel on x coordinate)
s = 2 / PMap( 1, 0 )
'' plot the function
For x = -1 To 1 Step s
y = x ^ 3
PSet( x, y ), 14
Next x
'' revert to screen coordinates
Window
'' remove the clipping area
View
'' draw title
Draw String ( 120, 160 ), "Y = X ^ 3"
Sleep
4、在内存中绘像素后显示在屏幕窗口
image pixel ， 简写 ip，ip = ImageCreate(64, 64)，在内存中创建一个64x64像素的像素块，ip是它的指针。
QBasic原有的PSet后面带上参数 ip, 表示在 ip 内存块pset像素点
screensync 是等待场同步信号，在换场的间隙中把图显示在屏幕窗口上，从而最大限度地减小抖动发生(这个语句的受限点是变换速度被限定在了场频之内)，在等待场同步时screenlock后绘图，绘好后screenunlock，将图显示到屏幕上，最后要imagedestroy(ip)销毁创建的像素块。因为在蓝框内有个view, 在view中显示的像素块。
'' examples/manual/gfx/view.bas
''
'' Example extracted from the FreeBASIC Manual
'' from topic 'VIEW (GRAPHICS)'
''
'' See Also: https://www.freebasic.net/wiki/wikka.php?wakka=KeyPgViewgraphics
'' --------
Screen 12
Dim ip As Any Ptr
Dim As Integer x, y
'simple sprite
ip = ImageCreate(64,64)
For y = 0 To 63
For x = 0 To 63
PSet ip, (x, y), (x\4) Xor (y\4)
Next x
Next y
'viewport with blue border
Line (215,135)-(425,345), 1, bf
View (220,140)-(420,340)
'move sprite around the viewport
Do
x = 100*Sin(Timer*2.0)+50
y = 100*Sin(Timer*2.7)+50
ScreenSync
ScreenLock
'clear viewport and put image
Cls 1
Put (x, y), ip, PSet
ScreenUnlock
Loop While Inkey = ""
ImageDestroy(ip)
5、显示内存的考贝
screenres 创建屏幕窗口。screenset 1, 0 设置工作页为1页(0页为正在显示的画面)。screensync等待场同步信号。screencopy 将工作页面1考贝到显示页面0，完成显示一个移动的红方块。如果将一个跑步者的不同像素块放在不同的工作页面，然后随场同步显示，则是一幅跑步画面。
'' examples/manual/gfx/screenset.bas
''
'' Example extracted from the FreeBASIC Manual
'' from topic 'SCREENSET'
''
'' See Also: https://www.freebasic.net/wiki/wikka.php?wakka=KeyPgScreenset
'' --------
' Open graphics screen (320*200, 8bpp) with 2 pages
ScreenRes 320, 200, 8, 2
' Work on page 1 while displaying page 0
ScreenSet 1, 0
Dim As Integer x = -40
Do
'' Clear the screen, draw a box, update x
Cls
Line (x, 80)-Step(39, 39), 4, BF
x += 1: If (x > 319) Then x = -40
' Wait for vertical sync: only used to control refresh rate, can be put anywhere in the Do loop
ScreenSync
' Copy work page to visible page
ScreenCopy
Loop While Inkey = ""
6、显示窗口指针
一个正在显示的窗口，实际是一张像素块，它有对应的内存，而内存地址就是显示窗口的指针，在freebasic中用screenptr获得。screeninfo w, h, , bypp, pitch获得屏幕窗口的长、宽、色彩模式和一行的像素数(因此才能知道什么时候换行)，在cairo绘图时也会看到这个参数的使用。移动指针、放置数据，即得到欲显示的图像。
'' examples/manual/gfx/screenptr2.bas
''
'' Example extracted from the FreeBASIC Manual
'' from topic 'SCREENPTR'
''
'' See Also: https://www.freebasic.net/wiki/wikka.php?wakka=KeyPgScreenptr
'' --------
'Const SCREEN_WIDTH = 256, SCREEN_HEIGHT = 256
Const SCREEN_WIDTH = 1024, SCREEN_HEIGHT = 768
Dim As Long w, h, bypp, pitch
'' Make 32-bit screen.
ScreenRes SCREEN_WIDTH, SCREEN_HEIGHT, 32
'' Get screen info (w and h should match the constants above, bypp should be 4)
ScreenInfo w, h, , bypp, pitch
'' Get the address of the frame buffer. An Any Ptr
'' is used here to allow simple pointer arithmetic
Dim buffer As Any Ptr = ScreenPtr()
If (buffer = 0) Then
Print "Error: graphics screen not initialized."
Sleep
End -1
End If
'' Lock the screen to allow direct frame buffer access
ScreenLock()
'' Set row address to the start of the buffer
Dim As Any Ptr row = buffer
'' Iterate over all the pixels in the screen:
For y As Integer = 0 To h - 1
'' Set pixel address to the start of the row
'' It's a 32-bit pixel, so use a ULong Ptr
Dim As ULong Ptr pixel = row
For x As Integer = 0 To w - 1
'' Set the pixel value
*pixel = RGB(x, x Xor y, y)
'' Get the next pixel address
'' (ULong Ptr will increment by 4 bytes)
pixel += 1
Next x
'' Go to the next row
row += pitch
Next y
'' Unlock the screen.
ScreenUnlock()
'' Wait for the user to press a key before closing the program
Sleep
7、获得鼠标和键盘事件
需要 fbgfx.bi 支持，event 是freebasic中的一个type类，它含有事件的名称和附带参数。 Dim e as event 定义 e 为 event 类 ; if (screenEvent(@e)) then 是如果有事件发生; e.type 是查看发生的事件。 e.scancode 是查看键盘扫描码; e.ascii 是按下键的ascii值; e.dx, e.dy是鼠标的位置; e.button是按的左键或右键, 如果左右键同时按，被视为中间键。
'' examples/manual/gfx/screenevent.bas
''
'' Example extracted from the FreeBASIC Manual
'' from topic 'SCREENEVENT'
''
'' See Also: https://www.freebasic.net/wiki/wikka.php?wakka=KeyPgScreenevent
'' --------
'' include fbgfx.bi for some useful definitions
#include "fbgfx.bi"
#if __FB_LANG__ = "fb"
Using fb '' constants and structures are stored in the FB namespace in lang fb
#endif
Dim e As Event
ScreenRes 640, 480
Do
If (ScreenEvent(@e)) Then
Select Case e.type
Case EVENT_KEY_PRESS
If (e.scancode = SC_ESCAPE) Then
End
End If
If (e.ascii > 0) Then
Print "'" & e.ascii & "'";
Else
Print "unknown key";
End If
Print " was pressed (scancode " & e.scancode & ")"
Case EVENT_KEY_RELEASE
If (e.ascii > 0) Then
Print "'" & e.ascii & "'";
Else
Print "unknown key";
End If
Print " was released (scancode " & e.scancode & ")"
Case EVENT_KEY_REPEAT
If (e.ascii > 0) Then
Print "'" & e.ascii & "'";
Else
Print "unknown key";
End If
Print " is being repeated (scancode " & e.scancode & ")"
Case EVENT_MOUSE_MOVE
Print "mouse moved to " & e.x & "," & e.y & " (delta " & e.dx & "," & e.dy & ")"
Case EVENT_MOUSE_BUTTON_PRESS
If (e.button = BUTTON_LEFT) Then
Print "left";
ElseIf (e.button = BUTTON_RIGHT) Then
Print "right";
Else
Print "middle";
End If
Print " button pressed"
Case EVENT_MOUSE_BUTTON_RELEASE
If (e.button = BUTTON_LEFT) Then
Print "left";
ElseIf (e.button = BUTTON_RIGHT) Then
Print "right";
Else
Print "middle";
End If
Print " button released"
Case EVENT_MOUSE_DOUBLE_CLICK
If (e.button = BUTTON_LEFT) Then
Print "left";
ElseIf (e.button = BUTTON_RIGHT) Then
Print "right";
Else
Print "middle";
End If
Print " button double clicked"
Case EVENT_MOUSE_WHEEL
Print "mouse wheel moved to position " & e.z
Case EVENT_MOUSE_ENTER
Print "mouse moved into program window"
Case EVENT_MOUSE_EXIT
Print "mouse moved out of program window"
Case EVENT_WINDOW_GOT_FOCUS
Print "program window got focus"
Case EVENT_WINDOW_LOST_FOCUS
Print "program window lost focus"
Case EVENT_WINDOW_CLOSE
End
Case EVENT_MOUSE_HWHEEL
Print "horizontal mouse wheel moved to position " & e.w
End Select
End If
Sleep 1
Loop
至此，应该可以写个简单的石头剪刀布游戏了。
