Implement map dragging and zooming

src/client/client.c

@@ -83,6 +83,68 @@ SDL_AppEvent (void *appstate, SDL_Event *event)
       return SDL_APP_SUCCESS;
     }
 
+  /* TODO: implement an event manager so this isn't in the main client
+     file. */
+
+  static bool dragging = false;
+  static float drag_start_x = 0, drag_start_y = 0;
+  static float drag_origin_x = 0, drag_origin_y = 0;
+
+  if (event->type == SDL_EVENT_MOUSE_BUTTON_DOWN &&
+      event->button.button == SDL_BUTTON_LEFT)
+    {
+      dragging = true;
+      drag_start_x = event->button.x;
+      drag_start_y = event->button.y;
+      drag_origin_x = gfx_ctx->world_x_offset;
+      drag_origin_y = gfx_ctx->world_y_offset;
+    }
+  else if (event->type == SDL_EVENT_MOUSE_BUTTON_UP &&
+           event->button.button == SDL_BUTTON_LEFT)
+    {
+      dragging = false;
+    }
+  else if (event->type == SDL_EVENT_MOUSE_MOTION && dragging)
+    {
+      float dx = event->motion.x - drag_start_x;
+      float dy = event->motion.y - drag_start_y;
+      gfx_ctx->world_x_offset = drag_origin_x + dx;
+      gfx_ctx->world_y_offset = drag_origin_y + dy;
+    }
+
+  if (event->type == SDL_EVENT_MOUSE_WHEEL)
+    {
+      float zoom_factor = 1.0f + (event->wheel.y * 0.1f); /* ±10% per notch */
+
+      /* Zoom around the mouse cursor */
+      int win_w, win_h;
+      SDL_GetWindowSize (gfx_ctx->window, &win_w, &win_h);
+
+      float mouse_x = event->wheel.mouse_x;
+      float mouse_y = event->wheel.mouse_y;
+
+      float before_x = (mouse_x - gfx_ctx->world_x_offset) / gfx_ctx->world_scale;
+      float before_y = (mouse_y - gfx_ctx->world_y_offset) / gfx_ctx->world_scale;
+
+      gfx_ctx->world_scale *= zoom_factor;
+
+      if (gfx_ctx->world_scale < 0.1f)
+	{
+	  gfx_ctx->world_scale = 0.1f; /* clamp */
+	}
+      
+      if (gfx_ctx->world_scale > 10.0f)
+	{
+	  gfx_ctx->world_scale = 10.0f;
+	}
+
+      float after_x = before_x * gfx_ctx->world_scale;
+      float after_y = before_y * gfx_ctx->world_scale;
+
+      gfx_ctx->world_x_offset = mouse_x - after_x;
+      gfx_ctx->world_y_offset = mouse_y - after_y;
+    }  
+
   return SDL_APP_CONTINUE;
 }
 

src/client/gfx_context.c

@@ -42,6 +42,8 @@ GfxContext_new ()
 		  SDL_GetError ());
     }
 
+  GfxContext_reset (self);
+  
   return self;
 }
 
@@ -53,12 +55,30 @@ GfxContext_render (GfxContext *self)
 
   if (self->world_texture)
     {
-      SDL_RenderTexture (self->renderer, self->world_texture, NULL, NULL);
+      float tex_w, tex_h;
+      SDL_GetTextureSize (self->world_texture, &tex_w, &tex_h);
+      
+      SDL_FRect dst = {
+        .x = self->world_x_offset,
+        .y = self->world_y_offset,
+        .w = tex_w * self->world_scale,
+        .h = tex_h * self->world_scale
+      };
+
+      SDL_RenderTexture (self->renderer, self->world_texture, NULL, &dst);
     }
 
   SDL_RenderPresent (self->renderer);
 }
 
+void
+GfxContext_reset (GfxContext *self)
+{
+  self->world_scale = 1.0;
+  self->world_x_offset = 0.0;
+  self->world_y_offset = 0.0;
+}
+
 void
 GfxContext_free (GfxContext *self)
 {
@@ -99,7 +119,9 @@ GfxContext_cache_World (GfxContext *self, World *world)
 	    g_array_index (world->tiles, MapTile *, y * world->width + x);
 
 	  if (!mt)
-	    continue;
+	    {
+	      continue;
+	    }
 
 	  switch (mt->terrain_type)
 	    {

src/client/gfx_context.h

@@ -38,10 +38,12 @@ typedef struct GfxContext
 				   and it could be done
 				   concurrently. */
 
+  float world_scale, world_x_offset, world_y_offset;
 } GfxContext;
 
 GfxContext *GfxContext_new ();
 void GfxContext_render (GfxContext * self);
+void GfxContext_reset (GfxContext *self);
 void GfxContext_free (GfxContext * self);
 
 void GfxContext_cache_World (GfxContext * self, World * world);