A rendering engine library for Go supporting both SDL2 and WebAssembly (HTML Canvas) targets.
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package render
import (
"fmt"
"math"
"git.kirsle.net/apps/doodle/lib/events"
)
// Engine is the interface for the rendering engine, keeping SDL-specific stuff
// far away from the core of Doodle.
type Engine interface {
Setup() error
// Poll for events like keypresses and mouse clicks.
Poll() (*events.State, error)
GetTicks() uint32
WindowSize() (w, h int)
// Present presents the current state to the screen.
Present() error
// Clear the full canvas and set this color.
Clear(Color)
SetTitle(string)
DrawPoint(Color, Point)
DrawLine(Color, Point, Point)
DrawRect(Color, Rect)
DrawBox(Color, Rect)
DrawText(Text, Point) error
ComputeTextRect(Text) (Rect, error)
// Texture caching.
NewBitmap(filename string) (Texturer, error)
Copy(t Texturer, src, dst Rect)
// Delay for a moment using the render engine's delay method,
// implemented by sdl.Delay(uint32)
Delay(uint32)
// Tasks that the Setup function should defer until tear-down.
Teardown()
Loop() error // maybe?
}
// Texturer is a stored image texture used by the rendering engine while
// abstracting away its inner workings.
type Texturer interface {
Size() Rect
}
// Rect has a coordinate and a width and height.
type Rect struct {
X int32
Y int32
W int32
H int32
}
// NewRect creates a rectangle of size `width` and `height`. The X,Y values
// are initialized to zero.
func NewRect(width, height int32) Rect {
return Rect{
W: width,
H: height,
}
}
func (r Rect) String() string {
return fmt.Sprintf("Rect<%d,%d,%d,%d>",
r.X, r.Y, r.W, r.H,
)
}
// Point returns the rectangle's X,Y values as a Point.
func (r Rect) Point() Point {
return Point{
X: r.X,
Y: r.Y,
}
}
// Bigger returns if the given rect is larger than the current one.
func (r Rect) Bigger(other Rect) bool {
// TODO: don't know why this is !
return !(other.X < r.X || // Lefter
other.Y < r.Y || // Higher
other.W > r.W || // Wider
other.H > r.H) // Taller
}
// Intersects with the other rectangle in any way.
func (r Rect) Intersects(other Rect) bool {
// Do a bidirectional compare.
compare := func(a, b Rect) bool {
var corners = []Point{
NewPoint(b.X, b.Y),
NewPoint(b.X, b.Y+b.H),
NewPoint(b.X+b.W, b.Y),
NewPoint(b.X+b.W, b.Y+b.H),
}
for _, pt := range corners {
if pt.Inside(a) {
return true
}
}
return false
}
return compare(r, other) || compare(other, r) || false
}
// IsZero returns if the Rect is uninitialized.
func (r Rect) IsZero() bool {
return r.X == 0 && r.Y == 0 && r.W == 0 && r.H == 0
}
// Add another rect.
func (r Rect) Add(other Rect) Rect {
return Rect{
X: r.X + other.X,
Y: r.Y + other.Y,
W: r.W + other.W,
H: r.H + other.H,
}
}
// Add a point to move the rect.
func (r Rect) AddPoint(other Point) Rect {
return Rect{
X: r.X + other.X,
Y: r.Y + other.Y,
W: r.W,
H: r.H,
}
}
// SubtractPoint is the inverse of AddPoint. Use this only if you need to invert
// the Point being added.
//
// This does r.X - other.X, r.Y - other.Y and keeps the width/height the same.
func (r Rect) SubtractPoint(other Point) Rect {
return Rect{
X: r.X - other.X,
Y: r.Y - other.Y,
W: r.W,
H: r.H,
}
}
// Text holds information for drawing text.
type Text struct {
Text string
Size int
Color Color
Padding int32
PadX int32
PadY int32
Stroke Color // Stroke color (if not zero)
Shadow Color // Drop shadow color (if not zero)
FontFilename string // Path to *.ttf file on disk
}
func (t Text) String() string {
return fmt.Sprintf(`Text<"%s" %dpx %s>`, t.Text, t.Size, t.Color)
}
// IsZero returns if the Text is the zero value.
func (t Text) IsZero() bool {
return t.Text == "" && t.Size == 0 && t.Color == Invisible && t.Padding == 0 && t.Stroke == Invisible && t.Shadow == Invisible
}
// Common color names.
var (
Invisible = Color{}
White = RGBA(255, 255, 255, 255)
Grey = RGBA(153, 153, 153, 255)
Black = RGBA(0, 0, 0, 255)
SkyBlue = RGBA(0, 153, 255, 255)
Blue = RGBA(0, 0, 255, 255)
DarkBlue = RGBA(0, 0, 153, 255)
Red = RGBA(255, 0, 0, 255)
DarkRed = RGBA(153, 0, 0, 255)
Green = RGBA(0, 255, 0, 255)
DarkGreen = RGBA(0, 153, 0, 255)
Cyan = RGBA(0, 255, 255, 255)
DarkCyan = RGBA(0, 153, 153, 255)
Yellow = RGBA(255, 255, 0, 255)
DarkYellow = RGBA(153, 153, 0, 255)
Magenta = RGBA(255, 0, 255, 255)
Purple = RGBA(153, 0, 153, 255)
Pink = RGBA(255, 153, 255, 255)
)
// IterLine is a generator that returns the X,Y coordinates to draw a line.
// https://en.wikipedia.org/wiki/Digital_differential_analyzer_(graphics_algorithm)
func IterLine(x1, y1, x2, y2 int32) chan Point {
generator := make(chan Point)
go func() {
var (
dx = float64(x2 - x1)
dy = float64(y2 - y1)
)
var step float64
if math.Abs(dx) >= math.Abs(dy) {
step = math.Abs(dx)
} else {
step = math.Abs(dy)
}
dx = dx / step
dy = dy / step
x := float64(x1)
y := float64(y1)
for i := 0; i <= int(step); i++ {
generator <- Point{
X: int32(x),
Y: int32(y),
}
x += dx
y += dy
}
close(generator)
}()
return generator
}
// IterLine2 works with two Points rather than four coordinates.
func IterLine2(p1 Point, p2 Point) chan Point {
return IterLine(p1.X, p1.Y, p2.X, p2.Y)
}