Add viewing area and ensure all images are displayed within it

src/main.c

@@ -4,6 +4,7 @@
 #include "tiffread.h"
 #include <SDL2/SDL.h>
 #include <SDL2/SDL_events.h>
+#include <SDL2/SDL_rect.h>
 #include <SDL2/SDL_render.h>
 #include <SDL2/SDL_surface.h>
 #include <SDL2/SDL_video.h>
@@ -18,6 +19,8 @@
 
 #define WINDOW_WIDTH 800
 #define WINDOW_HEIGHT 600
+#define VIEW_AREA_WIDTH 700
+#define VIEW_AREA_HEIGHT 500
 
 #define AMASK 0xff000000
 #define BMASK 0x00ff0000
@@ -34,6 +37,7 @@ struct point {
 
 internal void write_debug_ppm6(const Image *img);
 internal void *load_tiff_image(void *args);
+internal SDL_Rect get_dest_rect(SDL_Surface *surface);
 
 typedef struct img_thread_args ImgThreadArgs;
 struct img_thread_args {
@@ -90,12 +94,7 @@ int main(int argc, char *argv[]) {
     goto MAIN_DESTROY_SURFACE;
   }
 
-  SDL_Rect dest = {
-      .h = surface->h,
-      .w = surface->w,
-      .x = (WINDOW_WIDTH - surface->w) / 2,
-      .y = (WINDOW_HEIGHT - surface->h) / 2,
-  };
+  SDL_Rect dest = get_dest_rect(surface);
 
   bool running = true;
 
@@ -188,3 +187,16 @@ internal void *load_tiff_image(void *args) {
 
   return surface;
 }
+
+internal SDL_Rect get_dest_rect(SDL_Surface *surface) {
+  f64 ratio = (f64)(surface->h) / (f64)(surface->w);
+  u64 width = surface->w <= VIEW_AREA_WIDTH ? surface->w : VIEW_AREA_WIDTH;
+  u64 height = width * ratio;
+
+  return (SDL_Rect){
+      .w = width,
+      .h = height,
+      .x = (WINDOW_WIDTH - width) / 2,
+      .y = (WINDOW_HEIGHT - height) / 2,
+  };
+}