fix validation bugs. only remaining is screen tearing during resize

src/main.zig

@@ -76,6 +76,7 @@ pub fn create_swapchain(
 ) !vk.Extent2D {
     const extent = try gfx.find_swap_extent(pdev, vki, surface, window);
 
+    const prev_swapchain = swapchain.*;
     swapchain.* = try vkd.createSwapchainKHR(dev, &.{
         .surface = surface,
         .min_image_count = swap_image_count,
@@ -89,8 +90,9 @@ pub fn create_swapchain(
         .composite_alpha = .{ .opaque_bit_khr = true },
         .present_mode = present_mode,
         .clipped = vk.TRUE,
-        .old_swapchain = swapchain.*,
+        .old_swapchain = prev_swapchain,
     }, null);
+    vkd.destroySwapchainKHR(dev, prev_swapchain, null);
 
     var image_count: u32 = undefined;
     _ = try vkd.getSwapchainImagesKHR(dev, swapchain.*, &image_count, null);
@@ -351,6 +353,8 @@ pub fn main() !void {
                     try record_cmdbuf(cmdbuf, vkd, image, view, extent, pipeline, vertex_buffer, index_buffer);
                 }
 
+                index = 0;
+
                 continue;
             },
             else => |errx| return errx,