Add nine slice API

src/playdate/api.nim

@@ -7,8 +7,8 @@ import bindings/utils {.all.} as memory
 import bindings/api
 export api
 
-import graphics, system, file, sprite, display, sound, lua, json, utils, types
-export graphics, system, file, sprite, display, sound, lua, json, utils, types
+import graphics, system, file, sprite, display, sound, lua, json, utils, types, nineslice
+export graphics, system, file, sprite, display, sound, lua, json, utils, types, nineslice
 
 macro initSDK*() =
     return quote do:

src/playdate/nineslice.nim

@@ -0,0 +1,160 @@
+import graphics
+import std/[importutils, bitops, math, strutils]
+
+privateAccess(BitmapData)
+privateAccess(LCDBitmap)
+
+type
+    NineSliceRow {.byref.} = object
+        ## The bytes for a single row within a nine slice
+        leftBytes: seq[uint8]
+        middleBytes: seq[uint8]
+        rightBytes: seq[uint8]
+        leftRightBitLen: int
+
+    NineSliceData = ref object
+        ## Stores the rows for a single nine slice bitmap
+        top: seq[NineSliceRow]
+        middle: seq[NineSliceRow]
+        bottom: seq[NineSliceRow]
+
+    NineSlice* = ref object
+        ## A precalculated nine slice
+        image: NineSliceData
+        mask: NineSliceData
+
+func copyBits(
+    source: ptr UncheckedArray[uint8];
+    target: var seq[uint8];
+    sourceStartBit, sourceOffsetBit, sourceLen, targetStartBit, targetLen: int
+) =
+    ## Copies a sequence of bits from the source to the target, where all bit positions are absolute relative to
+    ## the start of the source or target
+    let minLength = ceil((targetStartBit + targetLen) / 8).toInt
+    target.setLen(max(target.len, minLength))
+
+    for bit in 0..<targetLen:
+        let sourceBit = sourceStartBit + ((bit + sourceOffsetBit) mod sourceLen)
+        let targetBit = targetStartBit + bit
+
+        if source[sourceBit div 8].testBit(7 - sourceBit mod 8):
+            target[targetBit div 8].setBit(7 - targetBit mod 8)
+
+func fillNineSliceRow(row: var NineSliceRow; source: BitmapData; y, leftRightBitLen: int) =
+    ## Each row gets a precalculated set of data that makes it faster to apply
+    let sourceStartBit = source.rowbytes * y * 8
+    let midSectionWidth = source.width - (2 * leftRightBitLen)
+
+    # Copy the bits for the leftmost column of the row
+    copyBits(source.data, row.leftBytes, sourceStartBit, 0, leftRightBitLen, 0, leftRightBitLen)
+
+    # If the leftmost bytes don't fill in to an even 8 bits, we pad it with bits from the center stretchable section.
+    # When drawing, this allows us to just blindly draw the first byte without any bit twiddling
+    copyBits(
+        source.data,
+        row.leftBytes,
+        sourceStartBit =    sourceStartBit + leftRightBitLen,
+        sourceOffsetBit =   0,
+        sourceLen =         midSectionWidth,
+        targetStartBit =    leftRightBitLen,
+        targetLen =         8 - (leftRightBitLen mod 8),
+    )
+
+    # Fills in the bytes for the middle section. We fill until the pattern repeats to reduce the amount of bit
+    # twiddling that needs to be done during render
+    copyBits(
+        source.data,
+        row.middleBytes,
+        sourceStartBit =    sourceStartBit + leftRightBitLen,
+        # Because the left bytes are filled in with some of the middle section bytes, we need to start copying
+        # bits at an offset that reflect the values that were already written. The following parameter is a calculation
+        # of what bit we left off on
+        sourceOffsetBit =   (8 - (leftRightBitLen mod 8)) mod midSectionWidth,
+        sourceLen =         midSectionWidth,
+        targetStartBit =    0,
+        targetLen =         midSectionWidth * 8,
+    )
+
+    # Fill the bytes for the right side of the nine slice
+    copyBits(source.data, row.rightBytes, sourceStartBit + source.width - leftRightBitLen, 0, leftRightBitLen, 0, leftRightBitLen)
+    row.leftRightBitLen = leftRightBitLen
+
+func createNineSliceData(source: BitmapData): NineSliceData =
+    ## Precalculates rendering instructions for a single bitmap
+    let leftRightBitLen = source.width div 3
+    let sliceHeight = source.height div 3
+
+    result = NineSliceData(
+        top: newSeq[NineSliceRow](sliceHeight),
+        middle: newSeq[NineSliceRow](source.height - sliceHeight * 2),
+        bottom: newSeq[NineSliceRow](sliceHeight),
+    )
+
+    # Precalculate the rows for the top and bottom sections
+    for i in 0..<sliceHeight:
+        result.top[i].fillNineSliceRow(source, i, leftRightBitLen)
+        result.bottom[i].fillNineSliceRow(source, source.height - sliceHeight + i, leftRightBitLen)
+
+    # Precalculate the rows for the stretchy middle section
+    for i in 0..<(source.height - sliceHeight * 2):
+        result.middle[i].fillNineSliceRow(source, sliceHeight + i, leftRightBitLen)
+
+proc newNineSlice*(source: LCDBitmap): NineSlice =
+    ## Precalculates a drawable nine slice from an image: https://en.wikipedia.org/wiki/9-slice_scaling
+    assert(source.width >= 3)
+    assert(source.height >= 3)
+    return NineSlice(
+        image: createNineSliceData(source.getData),
+        mask: if source.getBitmapMask.resource == nil: nil else: createNineSliceData(source.getBitmapMask.getData)
+    )
+
+func overlapBytes(left, right: uint8, offset: int): uint8 =
+    ## Given two bytes, creates a new byte that is partially made up of the left byte, and partially made up of
+    ## the right hand byte. The amount taken from each is determined by the `offset`
+    let leftContribution = left shl (8 - offset)
+    let rightContribution = right shr offset
+    result = leftContribution or rightContribution
+
+func drawRow(target: var BitmapData, source: NineSliceRow, targetY: int) =
+    ## Draws a single row to a nine slice.
+    let targetOffsetByte = target.rowbytes * targetY
+
+    # Draw the left column, a byte at a time
+    for i, byteValue in source.leftBytes:
+        target.data[i + targetOffsetByte] = byteValue
+
+    # Draw the stretched out middle column
+    let imageWidthInBytes = target.width div 8
+    let middleBytesLen = imageWidthInBytes - (2 * (source.leftRightBitLen div 8))
+    for i in 0..<middleBytesLen:
+        target.data[i + targetOffsetByte + source.leftBytes.len] = source.middleBytes[i mod source.middleBytes.len]
+
+    # Draw the right column, but we need to do some twiddling to align it properly. The position of the right column
+    # isn't something we can align ahead of time, so once we draw the left and middle portions, we need to overlay the
+    # right column and adjust its alignment
+    let rightColStartByte = (target.width - source.leftRightBitLen) div 8
+    let overlapBits = (target.width - source.leftRightBitLen) mod 8
+    var existingByte = target.data[targetOffsetByte + rightColStartByte] shr (8 - overlapBits)
+    for i in 0..(imageWidthInBytes - rightColStartByte):
+        let rightByte = source.rightBytes[min(i, source.rightBytes.len - 1)]
+        target.data[targetOffsetByte + rightColStartByte + i] = overlapBytes(existingByte, rightByte, overlapBits)
+        existingByte = rightByte
+
+func drawData(target: var BitmapData; source: NineSliceData) =
+    ## Draws a nine slice to a single bitmap target
+    for i in 0..<source.top.len:
+        target.drawRow(source.top[i], i)
+
+    for i in 0..<(target.height - source.top.len - source.bottom.len):
+        target.drawRow(source.middle[i mod source.middle.len], source.top.len + i)
+
+    for i in 0..<source.bottom.len:
+        target.drawRow(source.bottom[i], target.height - source.bottom.len + i)
+
+proc draw*(target: var LCDBitmap; source: NineSlice) =
+    ## Draws a nine slice to an image
+    var data = target.getData
+    drawData(data, source.image)
+    if source.mask != nil and target.getBitmapMask.resource != nil:
+        var maskData = target.getBitmapMask.getData
+        drawData(maskData, source.mask)

tests/src/playdate_tests.nim

@@ -5,13 +5,13 @@
 ##
 
 import playdate/api
-import ../t_buttons
-import ../t_graphics
+import ../[t_buttons, t_graphics, t_nineslice]
 
 proc runTests() {.raises: [].} =
     try:
         execButtonsTests()
         execGraphicsTests(true)
+        execNineSliceTests(true)
     except Exception as e:
         quit(e.msg & "\n" & e.getStackTrace)