Getting tile data from overworld

src/duskgl/display/shader/fragments/packed.glsl

@@ -4,13 +4,33 @@
 // https://opensource.org/licenses/MIT
 
 #define PACKED_U8_PER_UI 4
-#define PACKED_U8_PER_UVEC4 PACKED_U8_PER_UI / 4
+#define PACKED_U8_PER_UVEC4 PACKED_U8_PER_UI * 4
 
 uint packedGetU8(uint position, uint data) {
   return (data >> (position * 8u)) & 0xFFu;
 }
 
+uint packedGetU8FromVEC4(uint position, vec4 data) {
+  return packedGetU8(position, uint(data[position / 4u]));
+}
+
 int packedGetI8(uint position, uint data) {
   int shift = int(position * 8u);
   return int(data << (24 - shift)) >> 24;
+}
+
+uint packedArrayGetU8IndexFromUVEC4Array(uint u8ArrayIndex) {
+  // Given a uint8_t array is uploaded, this will return the index to get the
+  // appropriate uvec4 from a uvec4 array that will be at the right index.
+  return u8ArrayIndex / uint(PACKED_U8_PER_UVEC4);
+}
+
+uint packedArrayGetU8FromUVEC4ArrayValue(uint u8ArrayIndex, uvec4 data) {
+  // Given a value from a uint8_t array, this will return the value at the
+  // appropriate index. You must first get the uvec4 from the array using
+  // packedArrayGetU8IndexFromUVEC4Array.
+  uint subIndex = (u8ArrayIndex % uint(PACKED_U8_PER_UVEC4)) / uint(PACKED_U8_PER_UI);
+  uint shiftAmount = (u8ArrayIndex % uint(PACKED_U8_PER_UI)) * 8u;
+  uint value = (data[subIndex] >> shiftAmount) & 0xFFu;
+  return value;
 }