A rendering engine library for Go supporting both SDL2 and WebAssembly (HTML Canvas) targets.
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package render
import (
"fmt"
"regexp"
"strconv"
)
var regexpResolution = regexp.MustCompile(`^(\d+)x(\d+)$`)
// ParseResolution turns a resolution string like "1024x768" and returns the
// width and height values.
func ParseResolution(resi string) (int, int, error) {
m := regexpResolution.FindStringSubmatch(resi)
if m == nil {
return 0, 0, fmt.Errorf("invalid resolution format, should be %s",
regexpResolution.String(),
)
}
width, err := strconv.Atoi(m[1])
if err != nil {
return 0, 0, err
}
height, err := strconv.Atoi(m[2])
if err != nil {
return 0, 0, err
}
return width, height, nil
}
// TrimBox helps with Engine.Copy() to trim a destination box so that it
// won't overflow with the parent container.
func TrimBox(src, dst *Rect, p Point, S Rect, thickness int) {
// Constrain source width to not bigger than Canvas width.
if src.W > S.W {
src.W = S.W
}
if src.H > S.H {
src.H = S.H
}
// If the destination width will cause it to overflow the widget
// box, trim off the right edge of the destination rect.
//
// Keep in mind we're dealing with chunks here, and a chunk is
// a small part of the image. Example:
// - Canvas is 800x600 (S.W=800 S.H=600)
// - Chunk wants to render at 790,0 width 100,100 or whatever
// dst={790, 0, 100, 100}
// - Chunk box would exceed 800px width (X=790 + W=100 == 890)
// - Find the delta how much it exceeds as negative (800 - 890 == -90)
// - Lower the Source and Dest rects by that delta size so they
// stay proportional and don't scale or anything dumb.
if dst.X+src.W > p.X+S.W {
// NOTE: delta is a negative number,
// so it will subtract from the width.
delta := (p.X + S.W - thickness) - (dst.W + dst.X)
src.W += delta
dst.W += delta
}
if dst.Y+src.H > p.Y+S.H {
// NOTE: delta is a negative number
delta := (p.Y + S.H - thickness) - (dst.H + dst.Y)
src.H += delta
dst.H += delta
}
// The same for the top left edge, so the drawings don't overlap
// menu bars or left side toolbars.
// - Canvas was placed 80px from the left of the screen.
// Canvas.MoveTo(80, 0)
// - A texture wants to draw at 60, 0 which would cause it to
// overlap 20 pixels into the left toolbar. It needs to be cropped.
// - The delta is: p.X=80 - dst.X=60 == 20
// - Set destination X to p.X to constrain it there: 20
// - Subtract the delta from destination W so we don't scale it.
// - Add 20 to X of the source: the left edge of source is not visible
if dst.X < p.X {
// NOTE: delta is a positive number,
// so it will add to the destination coordinates.
delta := p.X - dst.X
dst.X = p.X + thickness
dst.W -= delta
src.X += delta
}
if dst.Y < p.Y {
delta := p.Y - dst.Y
dst.Y = p.Y + thickness
dst.H -= delta
src.Y += delta
}
// Trim the destination width so it doesn't overlap the Canvas border.
if dst.W >= S.W-thickness {
dst.W = S.W - thickness
}
}
// AbsInt returns the absolute value of an integer.
func AbsInt(v int) int {
if v < 0 {
return -v
}
return v
}
// AbsInt32 returns the absolute value of an int32.
func AbsInt32(v int32) int32 {
if v < 0 {
return -v
}
return v
}