api/texture: Have the first mip level be a reference to the base image

samples/texture-painting/texture-painting.js

@@ -122,5 +122,11 @@ function paint()
         realY += deltaY;
     }
 
-    this.texture.refresh();
+    // Since we modified the texture's pixels, we should call texture.refresh() to
+    // update all of the texture's mip levels with the new pixel data. However, in
+    // this rendering sample, we only ever display the first mip level (which is
+    // the base image), so we can save some performance by not refreshing the other
+    // mip levels.
+    //
+    //this.texture.refresh();
 }

src/api/texture.mjs

@@ -78,12 +78,11 @@ const schema = {
             "width": ["number"],
             "height": ["number"],
             "pixels": ["Uint8ClampedArray"],
-            "mipLevels": [["object"]],
+            "mipLevels": [["object", "Texture"]],
         },
     },
 };
 
-// Texture with 32-bit color.
 export function Texture(data = {})
 {
     data = structuredClone(data);
@@ -206,9 +205,23 @@ function decode_pixel_data(data)
 // full-resolution texture, and mipmaps[mipmaps.length-1] is the smallest, 1 x 1 texture.
 function regenerate_mipmaps()
 {
-    this.mipLevels = [];
+    Assert?.(
+        this.hasOwnProperty("$constructor") &&
+        (this.$constructor === "Texture"),
+        "Expected 'this' to point to a Texture"
+    );
+
+    // The first mip level is the base image, so we can just reference the base data.
+    this.mipLevels = [this];
+
+    if (
+        (this.width === 1) &&
+        (this.height === 1)
+    ){
+        return;
+    }
 
-    for (let m = 0; ; m++)
+    for (let m = 1; ; m++)
     {
         const mipWidth = Math.max(1, Math.floor(this.width / Math.pow(2, m)));
         const mipHeight = Math.max(1, Math.floor(this.height / Math.pow(2, m)));