gg: add cubic Bézier curves + examples (#11286)

pull/11291/head
Larpon 2021-08-24 05:35:27 +02:00 committed by GitHub
parent 3249f8f0e7
commit 833bf2cf15
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3 changed files with 147 additions and 0 deletions

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@ -0,0 +1,35 @@
module main
import gg
import gx
const (
p1_and_p2 = [f32(200.0), 200.0, 400.0, 300.0]
ctrl_p1_and_p2 = [f32(200.0), 100.0, 400.0, 100.0]
)
struct App {
mut:
gg &gg.Context
}
fn main() {
mut app := &App{
gg: 0
}
app.gg = gg.new_context(
bg_color: gx.rgb(174, 198, 255)
width: 600
height: 400
window_title: 'Cubic Bézier curve'
frame_fn: frame
user_data: app
)
app.gg.run()
}
fn frame(mut app App) {
app.gg.begin()
app.gg.draw_cubic_bezier(p1_and_p2, ctrl_p1_and_p2, gx.blue)
app.gg.end()
}

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@ -0,0 +1,60 @@
module main
import gg
import gx
const rate = f32(1) / 60 * 10
struct App {
mut:
gg &gg.Context
anim &Anim
}
struct Anim {
mut:
time f32
reverse bool
}
fn (mut anim Anim) advance() {
if anim.reverse {
anim.time -= 1 * rate
} else {
anim.time += 1 * rate
}
// Use some arbitrary value that fits 60 fps
if anim.time > 80 * rate || anim.time < -80 * rate {
anim.reverse = !anim.reverse
}
}
fn main() {
mut app := &App{
gg: 0
anim: &Anim{}
}
app.gg = gg.new_context(
bg_color: gx.rgb(174, 198, 255)
width: 600
height: 400
window_title: 'Animated cubic Bézier curve'
frame_fn: frame
user_data: app
)
app.gg.run()
}
fn frame(mut app App) {
time := app.anim.time
ctrl_p1_x := f32(200.0) + (40 * time)
ctrl_p2_x := f32(400.0) + (-40 * time)
p1_and_p2 := [f32(200.0), 200.0 + (10 * time), 400.0, 200.0 + (10 * time)]
app.gg.begin()
app.gg.draw_cubic_bezier(p1_and_p2, [ctrl_p1_x, 100.0, ctrl_p2_x, 100.0], gx.blue)
app.gg.end()
app.anim.advance()
}

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@ -674,6 +674,58 @@ pub fn (ctx &Context) draw_empty_poly(points []f32, c gx.Color) {
sgl.end() sgl.end()
} }
// draw_cubic_bezier draws a cubic Bézier curve, also known as a spline, from four points.
// The four points is provided as two arrays; `points` and `control_points`, which is both pairs of x and y coordinates.
// Thus a coordinate pair could be declared like: `points := [x1, y1, x2, y2]`.
// Please see `draw_cubic_bezier_in_steps` to control the amount of steps (segments) used to draw the curve.
pub fn (ctx &Context) draw_cubic_bezier(points []f32, control_points []f32, c gx.Color) {
ctx.draw_cubic_bezier_in_steps(points, control_points, u32(30 * ctx.scale), c)
}
// draw_cubic_bezier_in_steps draws a cubic Bézier curve, also known as a spline, from four points.
// The smoothness of the curve can be controlled with the `steps` parameter. `steps` determines how many iterations is
// taken to draw the curve.
// The four points is provided as two arrays; `points` and `control_points`, which is both pairs of x and y coordinates.
// Thus a coordinate pair could be declared like: `points := [x1, y1, x2, y2]`.
pub fn (ctx &Context) draw_cubic_bezier_in_steps(points []f32, control_points []f32, steps u32, c gx.Color) {
assert steps > 0
assert points.len == 4
assert points.len == control_points.len
if c.a != 255 {
sgl.load_pipeline(ctx.timage_pip)
}
sgl.c4b(c.r, c.g, c.b, c.a)
sgl.begin_line_strip()
p1_x, p1_y := points[0], points[1]
p2_x, p2_y := points[2], points[3]
ctrl_p1_x, ctrl_p1_y := control_points[0], control_points[1]
ctrl_p2_x, ctrl_p2_y := control_points[2], control_points[3]
// The constant 3 is actually points.len() - 1;
step := f32(1.0) / steps
sgl.v2f(p1_x * ctx.scale, p1_y * ctx.scale)
for u := f32(0.0); u <= f32(1.0); u += step {
pow_2_u := u * u
pow_3_u := pow_2_u * u
x := pow_3_u * (p2_x + 3 * (ctrl_p1_x - ctrl_p2_x) - p1_x) +
3 * pow_2_u * (p1_x - 2 * ctrl_p1_x + ctrl_p2_x) + 3 * u * (ctrl_p1_x - p1_x) + p1_x
y := pow_3_u * (p2_y + 3 * (ctrl_p1_y - ctrl_p2_y) - p1_y) +
3 * pow_2_u * (p1_y - 2 * ctrl_p1_y + ctrl_p2_y) + 3 * u * (ctrl_p1_y - p1_y) + p1_y
sgl.v2f(x * ctx.scale, y * ctx.scale)
}
sgl.v2f(p2_x * ctx.scale, p2_y * ctx.scale)
sgl.end()
}
// window_size returns the `Size` of the active window // window_size returns the `Size` of the active window
pub fn window_size() Size { pub fn window_size() Size {
s := dpi_scale() s := dpi_scale()