How can I implement a zoom feature using these scaling techniques?

Question

Ryan McCombe · Accepted Answer

Implementing a zoom feature in SDL2 involves manipulating the rendering process to display a portion of your game world at a larger scale. Here's a step-by-step guide to create a basic zoom feature:

Define Zoom Parameters

First, let's define some variables to control our zoom:

1float zoomLevel = 1.0f;
2
3// Center of the screen
4SDL_FPoint zoomCenter = {400, 300};

Create a Zoom Function

We'll create a function to adjust the zoom level:

1void AdjustZoom(float delta) {
2  zoomLevel += delta;
3  zoomLevel = std::max(0.1f,
4                       std::min(
5                         zoomLevel, 5.0f));
6  // Limit zoom range
7}

Implement Zooming in Render Function

Now, let's modify our rendering function to apply the zoom:

1#include <SDL.h>
2
3#include <vector>
4
5class Image { /* ... */ };
23
24void RenderScene(SDL_Renderer* renderer,
25                 const std::vector<Image>&
26                 images) {
27  SDL_SetRenderDrawColor(renderer, 255, 255,
28                         255, 255);
29  SDL_RenderClear(renderer);
30
31  for (const auto& img : images) {
32    SDL_FRect srcRect = {
33      0, 0, static_cast<float>(img.width),
34      static_cast<float>(img.height)};
35    SDL_FRect dstRect = srcRect;
36
37    // Apply zoom
38    dstRect.x = (dstRect.x - zoomCenter.x) *
39      zoomLevel + zoomCenter.x;
40    dstRect.y = (dstRect.y - zoomCenter.y) *
41      zoomLevel + zoomCenter.y;
42    dstRect.w *= zoomLevel;
43    dstRect.h *= zoomLevel;
44
45    SDL_RenderCopyF(renderer, img.texture,
46                    &srcRect, &dstRect);
47  }
48
49  SDL_RenderPresent(renderer);
50}

Handle Zoom Input

In your event handling loop, respond to user input to adjust the zoom:

1SDL_Event event;
2while (SDL_PollEvent(&event)) {
3  switch (event.type) {
4    case SDL_MOUSEWHEEL:
5      if (event.wheel.y > 0) {
6        AdjustZoom(0.1f);
7      } else if (event.wheel.y < 0) {
8        AdjustZoom(-0.1f);
9      }
10      break;
11      // Handle other events...
12  }
13}

Update Zoom Center (Optional)

For a more advanced zoom, you might want to update the zoom center based on mouse position:

1void UpdateZoomCenter(int mouseX, int mouseY) {
2  zoomCenter.x = mouseX;
3  zoomCenter.y = mouseY;
4}

1// In your event loop:
2case SDL_MOUSEMOTION:
3  UpdateZoomCenter(event.motion.x,
4                   event.motion.y);
5  break;

This implementation provides a basic zoom feature. You can further enhance it by adding smooth zooming, implementing pan functionality, or optimizing rendering for large game worlds.

Image Scaling and Aspect Ratios

Implementing a Zoom Feature in SDL2

Define Zoom Parameters

Create a Zoom Function

Implement Zooming in Render Function

Handle Zoom Input

Update Zoom Center (Optional)

Image Scaling and Aspect Ratios

Game Development with SDL2

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