Managing Window Position

Animated Window Movement

Can I smoothly animate a window moving from one position to another?

Abstract art representing computer programming

Yes! We can create smooth window animations by gradually updating the window position over time. Here's how to implement smooth window movement:

Basic Animation Implementation

Here’s a basic implementation of an AnimatedWindow class:

1// AnimatedWindow.h
2#pragma once
3#include <SDL.h>
4#include <chrono>
5#include "Window.h"
6
7using std::chrono::steady_clock,
8  std::chrono::duration;
9
10class AnimatedWindow : public Window {
11 public:
12  void AnimateTo(
13    int TargetX, int TargetY,
14    float DurationSeconds = 0.5f
15  ) {
16    // Get start position
17    SDL_GetWindowPosition(
18      SDLWindow, &StartX, &StartY);
19
20    // Set target and calculate distance
21    this->TargetX = TargetX;
22    this->TargetY = TargetY;
23
24    // Start animation
25    AnimationStart = steady_clock::now();
26    AnimationDuration = duration<float>(
27      DurationSeconds);
28    IsAnimating = true;
29  }
30
31  void Update() {
32    if (!IsAnimating) return;
33
34    // Calculate progress (0.0 to 1.0)
35    auto Now = steady_clock::now();
36    auto Elapsed = Now - AnimationStart;
37    float Progress = std::min(
38      1.0f, Elapsed / AnimationDuration);
39
40    // Use ease-out for smooth deceleration
41    float Smoothed = 1.0f - (1.0f - Progress)
42      * (1.0f - Progress);
43
44    // Calculate current position
45    int CurrentX = StartX + (TargetX - StartX)
46      * Smoothed;
47    int CurrentY = StartY + (TargetY - StartY)
48      * Smoothed;
49
50    // Update window position
51    SDL_SetWindowPosition(
52      SDLWindow, CurrentX, CurrentY);
53
54    // Check if animation is complete
55    if (Progress >= 1.0f) {
56      IsAnimating = false;
57    }
58  }
59
60 private:
61  bool IsAnimating{false};
62  int StartX{0}, StartY{0};
63  int TargetX{0}, TargetY{0};
64  steady_clock::time_point AnimationStart;
65  duration<float> AnimationDuration;
66};

Using the Animated Window

Here's how to use our animated window class:

1#include <SDL.h>
2#include <iostream>
3#include "AnimatedWindow.h"
4
5int main(int argc, char** argv) {
6  SDL_Init(SDL_INIT_VIDEO);
7  AnimatedWindow Window;
8  SDL_Event E;
9
10  // Center window initially
11  SDL_SetWindowPosition(Window.SDLWindow,
12                        SDL_WINDOWPOS_CENTERED,
13                        SDL_WINDOWPOS_CENTERED);
14
15  while (true) {
16    while (SDL_PollEvent(&E)) {
17      if (E.type == SDL_KEYDOWN) {
18        // Animate to corners on arrow key press
19        switch (E.key.keysym.sym) {
20        case SDLK_LEFT:
21          Window.AnimateTo(0, 300); 
22          break;
23        case SDLK_RIGHT:
24          Window.AnimateTo(800, 300);  
25          break;
26        }
27      }
28    }
29
30    Window.Update();
31  }
32
33  SDL_Quit();
34  return 0;
35}

Adding Different Animation Styles

We can create different animation feels by modifying the easing function:

1// Linear (constant speed)
2float Linear(float t) { return t; }
3
4// Ease-out (start fast, end slow)
5float EaseOut(float t) {
6  return 1.0f - (1.0f - t) * (1.0f - t);
7}
8
9// Ease-in (start slow, end fast)
10float EaseIn(float t) { return t * t; }
11
12// Bounce
13float Bounce(float t) {
14  if (t < 0.5f) {
15    return 4.0f * t * t * t;
16  } else {
17    float f = 2.0f * t - 2.0f;
18    return 0.5f * f * f * f + 1.0f;
19  }
20}

The key to smooth animation is:

Using time-based movement rather than frame-based
Implementing easing functions for natural acceleration/deceleration
Maintaining a consistent frame rate
Properly handling animation completion

Remember that frequent window updates can be resource-intensive, so use animation judiciously and consider providing an option to disable it for users who prefer instant movement.

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