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63 lines
1.5 KiB
Plaintext
63 lines
1.5 KiB
Plaintext
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#require "hbcairo"
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PROCEDURE Main()
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LOCAL hSurface, hCairo, nI
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hSurface := cairo_pdf_surface_create( "lightning.pdf", 566.9, 793.7 ) // 200x280 mm in pt
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hCairo := cairo_create( hSurface )
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// 20 pages
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FOR nI := 1 TO 20
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cairo_set_source_rgb( hCairo, 0, 0, 0 )
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cairo_paint( hCairo )
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cairo_set_source_rgb( hCairo, 1, 0.7, 1 )
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DrawLightning( hCairo, 250, 50, 700, 3 )
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cairo_show_page( hCairo )
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NEXT
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cairo_destroy( hCairo )
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cairo_surface_destroy( hSurface )
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RETURN
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PROCEDURE DrawLightning( hCairo, nX, nY, nLen, nW, nInit )
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LOCAL nI, nK, nW0, nX2
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cairo_move_to( hCairo, nX, nY )
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nW0 := nW
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IF nInit == NIL
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nInit := 0
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ENDIF
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nK := 0
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FOR nI := 1 TO nLen
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// AR(1) process
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nInit := nInit * 0.9 + ( hb_Random() - 0.5 )
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// ARIMA(1, 1, 0) process
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nK += nInit
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// ARIMA(1, 1, 0) + white noise
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nX2 := nX + nK + hb_Random()
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cairo_line_to( hCairo, nX2, nI + nY )
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nW -= 0.003
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IF nW < nW0 - 0.1
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cairo_set_line_width( hCairo, nW0 )
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cairo_stroke( hCairo )
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cairo_move_to( hCairo, nX2, nI + nY )
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nW0 := nW
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ENDIF
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// Branch
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IF Abs( nInit ) > 1.6
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cairo_set_line_width( hCairo, nW0 )
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cairo_stroke( hCairo )
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DrawLightning( hCairo, nX2, nI + nY, Int( ( nLen - nI ) / 2 ), nW / 2, nInit * 0.5 )
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nInit *= -0.3
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cairo_move_to( hCairo, nX2, nI + nY )
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ENDIF
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NEXT
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cairo_set_line_width( hCairo, nW0 )
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cairo_stroke( hCairo )
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RETURN
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