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examples/airship: Divide z to calculate scale

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Fixes #534
This commit is contained in:
Hajime Hoshi 2018-03-12 01:02:55 +09:00
parent 063153e41d
commit 56c4dbf28b
1 changed files with 9 additions and 45 deletions
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54
examples/airship/main.go
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@ -173,58 +173,22 @@ func updateGroundImage(ground *ebiten.Image) {
ground.DrawImage(repeatedGophersImage, op)
}
// scaleForLine calculates the scale to render at y-th line of the ground image.
func scaleForLine(y int) float64 {
// c |
// |\ |
// | \|
// | s
// | |\
// | | \
// A--B--C (plane)
//
// c: camera
// s: intersection of the ray and the screen
// A-c: camera height
// B-s: horizon height
// A-C: far point on the plane
// A-B: the distance from the camera to the screen
//
// The ground image is on the plane, and the head of the ground image is on 'C'.
const (
horizonHeight = screenHeight * 2.0 / 3.0
cameraHeight = horizonHeight + 100.0
farPointOnPlane = 200.0
cameraToScreen = farPointOnPlane - farPointOnPlane/cameraHeight*horizonHeight
)
s1 := cameraHeight / (farPointOnPlane - float64(y)) * (farPointOnPlane - float64(y) - cameraToScreen)
s2 := cameraHeight / (farPointOnPlane - float64(y+1)) * (farPointOnPlane - float64(y+1) - cameraToScreen)
if math.IsInf(s1, 0) || math.IsInf(s2, 0) {
return 0
}
return s1 - s2
}
func drawGroundImage(screen *ebiten.Image, ground *ebiten.Image) {
perspectiveGroundImage.Clear()
gw, gh := ground.Size()
gw, _ := ground.Size()
pw, ph := perspectiveGroundImage.Size()
y := 0.0
for i := 0; i < ph; i++ {
for j := 0; j < ph; j++ {
// z is in [1.5, 0.01]
rate := float64(j) / float64(ph)
z := (1-rate)*1.5 + rate*0.01
op := &ebiten.DrawImageOptions{}
s := scaleForLine(i)
dx0 := -float64(gw)*s/2 + float64(pw)/2
op.GeoM.Scale(s, s+1)
op.GeoM.Translate(float64(dx0), y)
op.GeoM.Translate(-float64(pw)/2, 0)
op.GeoM.Scale(1/z, 4) // 4 is an arbitrary number not to make empty lines.
op.GeoM.Translate(float64(pw)/2, float64(j)/z)
src := image.Rect(0, i, gw, i+1)
src := image.Rect(0, j, gw, j+1)
op.SourceRect = &src
perspectiveGroundImage.DrawImage(ground, op)
y += s
if y > float64(gh) {
break
}
}
perspectiveGroundImage.DrawImage(fogImage, nil)