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canvas.go
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canvas.go
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// © 2013 the Ui Authors under the MIT license. See AUTHORS for the list of authors.
package ui
/*
#include "ui.h"
*/
import "C"
import (
"image"
"image/color"
"image/png"
"os"
"unsafe"
)
// A Canvas can draw to a window.
// The drawing operations can only be safely used within the main go routine.
type Canvas struct {
win *Window
font font
}
// Clear clears the canvas with the drawing color.
func (c Canvas) Clear() {
if C.SDL_RenderClear(c.win.rend) < 0 {
panic(sdlError())
}
}
// SetColor sets the color used for drawing operations (DrawPoints, DrawLines, DrawRects, FillRects, and Clear).
func (c Canvas) SetColor(col color.Color) {
r, g, b, a := col.RGBA()
f := 255.0 / 0xFFFF
r8 := C.Uint8(float64(r) * f)
g8 := C.Uint8(float64(g) * f)
b8 := C.Uint8(float64(b) * f)
a8 := C.Uint8(float64(a) * f)
if C.SDL_SetRenderDrawColor(c.win.rend, r8, g8, b8, a8) < 0 {
panic(sdlError())
}
}
// Color returns the current drawing color.
func (c Canvas) color() color.Color {
var r, g, b, a C.Uint8
if C.SDL_GetRenderDrawColor(c.win.rend, &r, &g, &b, &a) < 0 {
panic(sdlError())
}
return color.NRGBA{uint8(r), uint8(g), uint8(b), uint8(a)}
}
// DrawPoints draws multiple points on the canvas.
func (c Canvas) DrawPoints(points ...image.Point) {
if C.SDL_RenderDrawPoints(c.win.rend, sdlPoints(points), C.int(len(points))) < 0 {
panic(sdlError())
}
}
// DrawLines draws a series of connected lines on the canvas.
func (c Canvas) DrawLines(points ...image.Point) {
if C.SDL_RenderDrawLines(c.win.rend, sdlPoints(points), C.int(len(points))) < 0 {
panic(sdlError())
}
}
func sdlPoints(points []image.Point) *C.SDL_Point {
pts := make([]C.SDL_Point, len(points))
for i, p := range points {
pts[i].x = C.int(p.X)
pts[i].y = C.int(p.Y)
}
return &pts[0]
}
// DrawRects draws some number of rectangles on the canvas.
func (c Canvas) DrawRects(rects ...image.Rectangle) {
if C.SDL_RenderDrawRects(c.win.rend, sdlRects(rects), C.int(len(rects))) < 0 {
panic(sdlError())
}
}
// FillRects fills some number of rectangles on the canvas with the drawing color.
func (c Canvas) FillRects(rects ...image.Rectangle) {
if C.SDL_RenderFillRects(c.win.rend, sdlRects(rects), C.int(len(rects))) < 0 {
panic(sdlError())
}
}
func sdlRects(rects []image.Rectangle) *C.SDL_Rect {
rs := make([]C.SDL_Rect, len(rects))
for i := range rects {
rs[i] = *sdlRect(&rects[i])
}
return &rs[0]
}
func sdlRect(rect *image.Rectangle) *C.SDL_Rect {
if rect == nil {
return nil
}
return &C.SDL_Rect{
x: C.int(rect.Min.X),
y: C.int(rect.Min.Y),
w: C.int(rect.Dx()),
h: C.int(rect.Dy()),
}
}
// DrawPNG draws the image loaded from a PNG file to the canvas.
// The image is drawn with the upper-left corner located at x, y.
func (c Canvas) DrawPNG(path string, x, y int) {
tex, ok := c.win.imgs[path]
if !ok {
img := loadPNG(path)
tex = texture{
tex: texFromImage(c.win.rend, img),
width: img.Bounds().Dx(),
height: img.Bounds().Dy(),
}
c.win.imgs[path] = tex
}
dst := image.Rect(x, y, x+tex.width, y+tex.height)
if C.SDL_RenderCopy(c.win.rend, tex.tex, nil, sdlRect(&dst)) < 0 {
panic(sdlError())
}
}
// SetFont sets the current font face and size (in points).
func (c *Canvas) SetFont(path string, size int) {
c.font = getFont(path, size)
}
// FillString fills a string of text in the current font and draw color. X and y specify the
// upper-left corner of the bounding box of the text, and the width and height of the
// bounding box is returned.
func (c Canvas) FillString(s string, x, y int) (width, height int) {
img := c.font.draw(s, c.color())
tex := texFromImage(c.win.rend, img)
defer C.SDL_DestroyTexture(tex)
b := img.Bounds()
w, h := b.Dx(), b.Dy()
dst := image.Rect(x, y, x+w, y+h)
if C.SDL_RenderCopy(c.win.rend, tex, nil, sdlRect(&dst)) < 0 {
panic(sdlError())
}
return w, h
}
// StringSize returns the width and height of the string in pixels when rendered in the current font.
func (c Canvas) StringSize(s string) (width, height int) {
height, _, _ = c.font.extents()
return c.font.width(s), height
}
func texFromImage(rend *C.SDL_Renderer, img *image.NRGBA) *C.SDL_Texture {
b := img.Bounds()
w, h := b.Dx(), b.Dy()
fmt := C.SDL_PIXELFORMAT_ABGR8888
acc := C.SDL_TEXTUREACCESS_STATIC
tex := C.SDL_CreateTexture(rend, C.Uint32(fmt), C.int(acc), C.int(w), C.int(h))
if tex == nil {
panic(sdlError())
}
if C.SDL_UpdateTexture(tex, nil, unsafe.Pointer(&img.Pix[0]), C.int(img.Stride)) < 0 {
panic(sdlError())
}
if C.SDL_SetTextureBlendMode(tex, C.SDL_BLENDMODE_BLEND) < 0 {
panic(sdlError())
}
return tex
}
func loadPNG(path string) *image.NRGBA {
r, err := os.Open(path)
if err != nil {
panic(err)
}
defer r.Close()
img, err := png.Decode(r)
if err != nil {
panic(err)
}
return img.(*image.NRGBA)
}