doodle/render/interface.go

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package render
import (
"fmt"
"math"
"git.kirsle.net/apps/doodle/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
// Present presents the current state to the screen.
Present() error
// Clear the full canvas and set this color.
Clear(Color)
DrawPoint(Color, Point)
DrawLine(Color, Point, Point)
DrawRect(Color, Rect)
DrawBox(Color, Rect)
DrawText(Text, Point) error
// 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?
}
// Color holds an RGBA color value.
type Color struct {
Red uint8
Green uint8
Blue uint8
Alpha uint8
}
// RGBA creates a new Color.
func RGBA(r, g, b, a uint8) Color {
return Color{
Red: r,
Green: g,
Blue: b,
Alpha: a,
}
}
func (c Color) String() string {
return fmt.Sprintf(
"Color<#%02x%02x%02x>",
c.Red, c.Green, c.Blue,
)
}
// Point holds an X,Y coordinate value.
type Point struct {
X int32
Y int32
}
func (p Point) String() string {
return fmt.Sprintf("Point<%d,%d>", p.X, p.Y)
}
// Rect has a coordinate and a width and height.
type Rect struct {
X int32
Y int32
W int32
H int32
}
func (r Rect) String() string {
return fmt.Sprintf("Rect<%d,%d,%d,%d>",
r.X, r.Y, r.W, r.H,
)
}
// Text holds information for drawing text.
type Text struct {
Text string
Size int
Color Color
Stroke Color // Stroke color (if not zero)
Shadow Color // Drop shadow color (if not zero)
}
func (t Text) String() string {
return fmt.Sprintf("Text<%s>", t.Text)
}
// 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)
}