69 lines
2.4 KiB
Standard ML
69 lines
2.4 KiB
Standard ML
structure TextScroll =
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struct
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structure TC = TextConstants
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(* calculates new scroll column from integer arguments *)
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fun calculateScrollColumn
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(startOfLine, cursorIdx, windowWidth, prevScrollColumn) =
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let
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val newColumn = cursorIdx - startOfLine
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val howManyColumnsCanWeFit =
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if windowWidth >= TC.textLineWidth then TC.textLineCount
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else windowWidth div TC.xSpace
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val howManyColumnsCanWeFit = howManyColumnsCanWeFit - 1
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in
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if newColumn < prevScrollColumn then
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(* we are moving the cursor backwards
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* so make sure that newColumn is on the left side *)
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newColumn
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else if newColumn > prevScrollColumn + howManyColumnsCanWeFit then
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(* we are scrolling forwards *)
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newColumn - howManyColumnsCanWeFit
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else
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(* we can display the current column without moving the scroll column
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* so we do that *)
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prevScrollColumn
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end
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(* Preqreuisite: move buffer to cursorIdx *)
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fun getScrollColumn (buffer, cursorIdx, windowWidth, prevScrollColumn) =
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let
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val startOfLine = Cursor.vi0 (buffer, cursorIdx)
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in
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calculateScrollColumn
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(startOfLine, cursorIdx, windowWidth, prevScrollColumn)
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end
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fun getScrollColumnFromString (cursorIdx, windowWidth, prevScrollColumn) =
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calculateScrollColumn (0, cursorIdx, windowWidth, prevScrollColumn)
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fun getStartLine (prevLineNumber, cursorLine, windowHeight, totalLines) =
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if cursorLine <= (prevLineNumber + 3) then
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(* cursorLine is prior to or same as prevLineNumber,
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* so use cursorLine to calculate the start line we want. *)
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Int.max (cursorLine - 3, 0)
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else
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(* cursorLine > prevLineNumber *)
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let
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val howManyLinesWeCanFit = windowHeight div TC.ySpace
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in
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if cursorLine > prevLineNumber + (howManyLinesWeCanFit - 3) then
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(* cursorLine is after the visible part of the screen
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* so return the mimimum line where cursorLine is visible *)
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if cursorLine >= totalLines - 3 then
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Int.max (totalLines - howManyLinesWeCanFit, 0)
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else
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cursorLine - howManyLinesWeCanFit + 3
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else
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prevLineNumber
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end
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fun getLineCentre (cursorLine, windowHeight) =
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let
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val howManyLinesWeCanFit = windowHeight div TC.ySpace
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val startLine = cursorLine - (howManyLinesWeCanFit div 2)
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in
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Int.max (startLine, 0)
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end
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end
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