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Task/Bitmap/Go/bitmap.go

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+// Raster package used with a number of RC tasks.
+//
+// For each task, documentation in package main source will list this
+// file and others that are necessary to build a raster package with
+// sufficient functionality for the task.  To build a working program,
+// build a raster package from the files listed, install the package,
+// and then compile and link the package main that completes the task.
+//
+// Alternatively, files in the raster package can be combined as desired
+// to build a package that meets the needs of multiple tasks.
+package raster
+
+// Rgb is a 24 bit color value represented with a 32 bit int
+// in the conventional way.  This is expected to be convenient
+// for the programmer in many cases.
+type Rgb int32
+
+// Pixel has r, g, and b as separate fields.  This is used as
+// the in-memory representation of a bitmap.
+type Pixel struct {
+    R, G, B byte
+}
+
+// Pixel returns a new Pixel from a Rgb value
+func (c Rgb) Pixel() Pixel {
+    return Pixel{R: byte(c >> 16), G: byte(c >> 8), B: byte(c)}
+}
+
+// Rgb returns a single Rgb value computed from rgb fields of a Pixel
+// of a Pixel.
+func (p Pixel) Rgb() Rgb {
+    return Rgb(p.R)<<16 | Rgb(p.G)<<8 | Rgb(p.B)
+}
+
+// Bitmap is the in-memory representation, or image storage type of a bitmap.
+// Zero value for type is a valid zero-size bitmap.
+// The only exported field is Comments.  Remaining fields have interdepencies
+// that are managed by package code and so should not be directly accessed
+// from outside the package.
+type Bitmap struct {
+    Comments   []string
+    rows, cols int
+    px         []Pixel   // all pixels as a single slice, row major order
+    pxRow      [][]Pixel // rows of pixels as slices of px
+}
+
+const creator = "# Creator: Rosetta Code http://rosettacode.org/"
+
+// New is a Bitmap "constructor."  Parameters x and y are extents.
+// That is, the new bitmap will have x columns and y rows.
+func NewBitmap(x, y int) (b *Bitmap) {
+    b = &Bitmap{
+        Comments: []string{creator},
+        rows:     y, // named fields here to prevent possible mix-ups.
+        cols:     x,
+        px:       make([]Pixel, x*y),
+        pxRow:    make([][]Pixel, y),
+    }
+    // Note rows of pixels are not allocated separately.
+    // Rather the whole bitmap is allocted in one chunk as px.
+    // This simplifies allocation and maintains locality.
+    x0, x1 := 0, x
+    for i := range b.pxRow {
+        b.pxRow[i] = b.px[x0:x1] // slice operation. does no allocation.
+        x0, x1 = x1, x1+x
+    }
+    return b
+}
+
+// Extent returns bitmap dimensions.
+func (b *Bitmap) Extent() (cols, rows int) {
+    return b.cols, b.rows
+}
+
+// Fill entire bitmap with solid color.
+func (b *Bitmap) Fill(p Pixel) {
+    for i := range b.px {
+        b.px[i] = p
+    }
+}
+
+func (b *Bitmap) FillRgb(c Rgb) {
+    b.Fill(c.Pixel())
+}
+
+// Set a single pixel color value.
+// Clips to bitmap boundaries.
+// Returns true if pixel was set, false if clipped.
+func (b *Bitmap) SetPx(x, y int, p Pixel) bool {
+    defer func() { recover() }()
+    b.pxRow[y][x] = p
+    return true
+}
+
+func (b *Bitmap) SetPxRgb(x, y int, c Rgb) bool {
+    return b.SetPx(x, y, c.Pixel())
+}
+
+// Note:  Clipping to bitmap boundaries is needed for program correctness
+// but is otherwise not required by the task.  It is implemented with the
+// combination of pxRow and the deferred recover.  SetPx, GetPx return the
+// clipping result as a way for higher level graphics functions to track
+// plotting and clipping status.  As this is not required by tasks though,
+// it is generally not implemented.
+
+// Get a single pixel color value.
+// Returns pixel and ok=true if coordinates are within bitmap boundaries.
+// Returns ok=false if coordinates are outside bitmap boundaries.
+func (b *Bitmap) GetPx(x, y int) (p Pixel, ok bool) {
+    defer func() { recover() }()
+    return b.pxRow[y][x], true
+}
+
+func (b *Bitmap) GetPxRgb(x, y int) (Rgb, bool) {
+    p, ok := b.GetPx(x, y)
+    if !ok {
+        return 0, false
+    }
+    return p.Rgb(), true
+}