Added save_track_file. Fixed bugs.

Encountered bug where incorrect tracks would be displayed if the loading process failed.
Added checksum validation to loading code.
Increased the max rle length to match rct2.

src/ride/track.c

@@ -508,7 +508,10 @@ rct_track_td6* load_track_design(const char *path)
 
 	// Validate the checksum
 	// Not the same checksum algorithm as scenarios and saved games
-	// sub_6770C1();
+	if (!sawyercoding_validate_track_checksum(fpBuffer, fpLength)){
+		log_error("Track checksum failed.");
+		return 0;
+	}
 
 	// Decode the track data
 	decoded = malloc(0x10000);
@@ -1055,6 +1058,8 @@ rct_track_design *track_get_info(int index, uint8** preview)
 
 		if (!(loaded_track = load_track_design(track_path))) {
 			if (preview != NULL) *preview = NULL;
+			// Mark cache as empty.
+			RCT2_ADDRESS(RCT2_ADDRESS_TRACK_DESIGN_INDEX_CACHE, uint32)[i] = 0;
 			log_error("Failed to load track: %s", trackDesignList + (index * 128));
 			return NULL;
 		}
@@ -1790,6 +1795,33 @@ int ride_to_td6(uint8 rideIndex){
 	return tracked_ride_to_td6(rideIndex, track_design, track_elements);
 }
 
+/* rct2: 0x006771DC but not really its branched from that
+ * quite far.
+ */
+int save_track_to_file(rct_track_td6* track_design, char* path){
+	window_close_construction_windows();
+
+	uint8* track_file = malloc(0x8000);
+
+	int length = sawyercoding_encode_td6((char*)track_design, track_file, 0x609F);
+
+	FILE *file;
+
+	log_verbose("saving track %s", path);
+	file = fopen(path, "wb");
+	if (file == NULL) {
+		free(track_file);
+		log_error("Failed to save %s", path);
+		return 0;
+	}
+
+	fwrite(track_file, length, 1, file);
+	fclose(file);
+	free(track_file);
+
+	return 1;
+}
+
 /* rct2: 0x006D2804 & 0x006D264D */
 int save_track_design(uint8 rideIndex){
 	rct_ride* ride = GET_RIDE(rideIndex);
@@ -1859,10 +1891,7 @@ int save_track_design(uint8 rideIndex){
 		return 1;
 	}
 
-	// Until 0x006771DC is finished we required to copy the path name.
-	strcpy(RCT2_ADDRESS(0x141EF68, char), path);
-	// This is the function that actually saves the track to a file
-	RCT2_CALLPROC_EBPSAFE(0x006771DC);
+	save_track_to_file(RCT2_ADDRESS(0x009D8178, rct_track_td6), path);
 
 	ride_list_item item = { .type = 0xFC, .entry_index = 0 };
 	track_load_list(item);

src/util/sawyercoding.c

@@ -225,6 +225,43 @@ int sawyercoding_decode_td6(char *src, char *dst, int length)
 	return decode_chunk_rle(src, dst, length - 4);
 }
 
+int sawyercoding_encode_td6(char* src, char* dst, int length){
+	int output_length = encode_chunk_rle(src, dst, length);
+
+	uint32 checksum = 0;
+	for (int i = 0; i < output_length; i++){
+		uint8 new_byte = ((checksum & 0xFF) + dst[i]) & 0xFF;
+		checksum = (checksum & 0xFFFFFF00) + new_byte;
+		checksum = rol32(checksum, 3);
+	}
+	checksum -= 0x1D4C1;
+
+	*((uint32*)&dst[output_length]) = checksum;
+	output_length += 4;
+	return output_length;
+}
+
+/* Based off of rct2: 0x006770C1 */
+int sawyercoding_validate_track_checksum(char* src, int length){
+	uint32 file_checksum = *((uint32*)&src[length - 4]);
+
+	uint32 checksum = 0;
+	for (int i = 0; i < length - 4; i++){
+		uint8 new_byte = ((checksum & 0xFF) + src[i]) & 0xFF;
+		checksum = (checksum & 0xFFFFFF00) + new_byte;
+		checksum = rol32(checksum, 3);
+	}
+
+	if (checksum - 0x1D4C1 == file_checksum)
+		return 1;	// .TD6
+	else if (checksum - 0x1A67C == file_checksum)
+		return 1;	// .TD4
+	else if (checksum - 0x1A650 == file_checksum)
+		return 1;	// .TD4 
+	else
+		return 0;
+}
+
 #pragma region Decoding
 
 /**
@@ -318,14 +355,14 @@ static int encode_chunk_rle(char *src_buffer, char *dst_buffer, int length)
 
 	while (src < end_src - 1){
 
-		if ((count && *src == src[1]) || count > 120){
+		if ((count && *src == src[1]) || count > 125){
 			*dst++ = count - 1;
 			for (; count != 0; --count){
 				*dst++ = *src_norm_start++;
 			}
 		}
 		if (*src == src[1]){
-			for (; (count < 120) && ((src + count) < end_src); count++){
+			for (; (count < 125) && ((src + count) < end_src); count++){
 				if (*src != src[count]) break;
 			}
 			*dst++ = 257 - count;

src/util/sawyercoding.h

@@ -55,6 +55,8 @@ int sawyercoding_decode_sv4(char *src, char *dst, int length);
 int sawyercoding_decode_sc4(char *src, char *dst, int length);
 int sawyercoding_encode_sv4(char *src, char *dst, int length);
 int sawyercoding_decode_td6(char *src, char *dst, int length);
+int sawyercoding_encode_td6(char* src, char* dst, int length);
+int sawyercoding_validate_track_checksum(char* src, int length);
 
 int sawyercoding_detect_file_type(char *src, int length);