前言

上一节讲了颜色调制, 这一节我们讲透明度的转换 由于透明度的变化会使得两张图片的融合, 我们还需要设置容和标志

代码

package main

import (
    "github.com/veandco/go-sdl2/img"
    "github.com/veandco/go-sdl2/sdl"
)

type Texture struct {
    t *sdl.Texture
}

func (this *Texture) LoadFromFile(path string) bool {
    img, err := img.Load(path)
    if err != nil {
        panic(err)
    }
    this.t, err = Grender.CreateTextureFromSurface(img)
    if err != nil {
        panic(err)
    }
    img.Free()

    return true
}

func (this *Texture) Render(x, y int32, src *sdl.Rect) {
    if src == nil {
        Grender.Copy(this.t, nil, nil)
    } else {
        dst := &sdl.Rect{X: x, Y: y, W: src.W, H: src.H}
        Grender.Copy(this.t, src, dst)
    }
}

func (this *Texture) setColor(r, g, b uint8) {
    this.t.SetColorMod(r, g, b)
}

func (this *Texture) SetAlpha(a uint8) {
    this.t.SetAlphaMod(a)
}

func (this *Texture) SetBlendMode(blend sdl.BlendMode) {
    this.t.SetBlendMode(blend)
}

func (this *Texture) Free() {
    this.t.Destroy()
}

const (
    W = 670
    H = 620
)

var (
    Gwindow     *sdl.Window
    Grender     *sdl.Renderer
    backTexture *Texture
    upTexture   *Texture
)

func init() {
    sdl.Init(sdl.INIT_EVERYTHING)
    Gwindow, err := sdl.CreateWindow("test", sdl.WINDOWPOS_UNDEFINED, sdl.WINDOWPOS_UNDEFINED, W, H, sdl.WINDOW_SHOWN)
    if err != nil {
        panic(err)
    }
    Grender, err = sdl.CreateRenderer(Gwindow, -1, sdl.RENDERER_ACCELERATED)
    if err != nil {
        panic(err)
    }
    Grender.SetDrawColor(128, 128, 128, 255)
    backTexture, upTexture = &Texture{}, &Texture{}
    backTexture.LoadFromFile("../asserts/image/fadein.png")
    upTexture.LoadFromFile("../asserts/image/fadeout.png")
    upTexture.SetBlendMode(sdl.BLENDMODE_BLEND)
}
func main() {
    a := 255

    running := true
    for running {
        for event := sdl.PollEvent(); event != nil; event = sdl.PollEvent() {
            switch t := event.(type) {
            case *sdl.QuitEvent:
                println("Quit")
                running = false
                break
            //case *sdl.KeyboardEvent:
            case *sdl.KeyboardEvent:
                if t.State == sdl.PRESSED {
                    switch t.Keysym.Sym {
                    case sdl.K_q:
                        if a+32 > 255 {
                            a = 255
                        } else {
                            a += 32
                        }
                        fmt.Println("alpha = ", a)
                    case sdl.K_w:
                        if a-32 < 0 {
                            a = 0
                        } else {
                            a -= 32
                        }
                    }
                }
            }
        }
        Grender.Clear()
        backTexture.Render(0, 0, nil)
        upTexture.SetAlpha(uint8(a))
        upTexture.Render(0, 0, nil)

        Grender.Present()
        sdl.Delay(16)
    }
    free()
}

func free() {
    backTexture.Free()
    upTexture.Free()
    Grender.Destroy()
    Gwindow.Destroy()
    sdl.Quit()
}

1. 首先在 Texture 结构体中添加两个方法, SetAlpha 和 SetBlendMode, 一个设置 alpha 值, 一个设置 blend 融合标志
2. 然后添加两张图片
3. 主循环里根据按键不同对 alpha 值进行修改, 最后渲染出来
4. 没有很多东西, 很容易理解

源码 https://gitee.com/fcsvr/tank.git