Hello everyone,
I’ve been working on a project that involves encoding Terraria world data into a PNG image using a C library and then displaying it in a Xojo Canvas. The process is functional, but I’ve encountered performance issues, especially with larger images (e.g., 8400x2400). The bottleneck seems to be the encode_png_image function, which takes a considerable amount of time.
Here’s a brief overview of the relevant parts of my code:
In C:
I have a C function encode_world_to_png that reads a Terraria world file, processes the data, and encodes it into a PNG image. The function returns a PNG image, but the encoding step is time-consuming.
// C Code
/**
* Encodes a Terraria world file to a PNG image.
* @param world_path The path to the Terraria world file.
* @param img_path The path to save the PNG image.
* @param is_mark_important Whether to mark important items in the image.
* @return 0 if successful, 1 otherwise.
*/
int encode_world_to_png(const char *world_path, const char *img_path, bool is_mark_important) {
FILE *fp;
Format format;
Header header;
fp = topen(world_path, "rb");
if (fp == NULL) {
printf("Failed to open file\n");
return 1;
}
parse_format(fp,&format);
parse_header(fp, &header, &format.version,format.pointers[0],format.pointers[1]);
// Call the read_tiles function
uint32_t width = header.Width;
uint32_t height = header.Height;
uint8_t *tiles_data;
int data_size;
// Read tile data
tiles_data = read_sections(fp, &format, 1, 2, &data_size);
if (tiles_data == NULL) {
printf("Failed to read tile data\n");
return 1;
}
// Calculate the total size of RLE data
int total_rle = width * height;
// Calculate the size of the required image buffer
size_t image_size = total_rle * 3; // Because RGB requires 3 bytes per pixel
// Allocate memory for the image buffer
unsigned char *image = malloc(image_size);
if (image == NULL)
{
printf("Error allocating memory for image buffer\n");
return 1;
}
set_pixels_color(image, tiles_data, &format, &header);
if (is_mark_important) {
uint8_t *chests_data;
// Read chest data
chests_data = read_sections(fp, &format, 2, 3, &data_size);
if (chests_data == NULL) {
printf("Failed to read chest data\n");
return 1;
}
ItemColor *item_colors = NULL;
create_item_colors_dict(&item_colors);
mark_important_items(image, chests_data, width, height, item_colors);
delete_item_colors_dict(&item_colors);
free(chests_data);
}
fclose(fp);
int ret = 0;
int bit_depth = 8;
enum spng_color_type color_type = SPNG_COLOR_TYPE_TRUECOLOR;
printf("image_size: %d\n", image_size);
ret = encode_png_image(img_path,image, image_size, width, height, color_type, bit_depth);
free_format(&format);
free_header(&header);
free(image);
return ret;
}
/**
* @brief Starts an asynchronous operation to encode a Terraria world file to a PNG image.
*
* @param world_path The path to the Terraria world file.
* @param img_path The path to save the PNG image.
* @param is_mark_important Whether to mark important items in the image.
* @param callback A pointer to the callback function to be called after the asynchronous operation completes. Can be NULL.
* @return 0 if successful, -1 otherwise.
*/
int encode_world_to_png_async_start(const char *world_path, const char *img_path, bool is_mark_important, Callback callback);
In Xojo:
I use the MBS Xojo Plugin to call the C functions from my Xojo application. I start the asynchronous encoding process using encode_world_to_png_async_start, and a callback function is executed once the operation completes.
' In Window1
Sub Opening()
CheckAndCreateTmpFolder
MyLibrary = New DeclareLibraryMBS("E:\libTerraDll.dll")
Dim lines() As String = MyLibrary.SymbolNames
MyCallback = New Callback("i)v")
End Sub
' In Button1
Sub Pressed()
Dim file As FolderItem = OpenFileDialogSeleteTerraWorld
If file <> Nil And file.Exists Then
worldFileName = file.Name.TrimRight(".wld",".bak",".wld.bak")
Dim imageFullName As CString = tmpFolderPath+"\"+worldFileName+".png"
Dim isMarkImportant As Boolean = isMarkChestsImportant.getBoolean
Dim worldFullName As CString = file.NativePath
Dim p As ptr = MyLibrary.Symbol("encode_world_to_png_async_start")
MyFounction = New DeclareFunctionMBS("(ZZBp)l", p)
MyFounction.ParameterString(0) = worldFullName
MyFounction.ParameterString(1) = imageFullName
MyFounction.ParameterBoolean(2) = isMarkImportant
MyFounction.ParameterPointer(3) = MyCallback.FunctionPtr
MyCallback.Result = 1
Timer1.Enabled = True
EncodeImageProgressBar.Visible = True
Dim r As Variant = MyFounction.Invoke
End If
End Sub
' In Timer1
Sub Action()
If MyCallback.Result = 0 Then
Dim file As FolderItem
Dim imageFullName As String = tmpFolderPath+"\"+worldFileName+".png"
file = New FolderItem(imageFullName)
If file <> Nil And file.Exists Then
img = Picture.Open(file)
imgHeight = img.Height
imgWidth = img.Width
scaleWidth = img.Width
scaleHeight = img.Height
hScrollBar.MaximumValue = imgWidth - imgCanvas.Width
vScrollBar.MaximumValue = imgHeight - imgCanvas.Height
imgCanvas.Refresh
Timer1.Enabled = False
EncodeImageProgressBar.Visible = False
End If
End If
End Sub
My Goal:
I’m looking for a more efficient approach to display Terraria world data in the Xojo Canvas. I’ve explored the possibility of directly setting pixel colors in C and passing them to Xojo without encoding to PNG. This would eliminate the time-consuming PNG encoding step.
One solution I considered was to set the pixel colors in C, bypass the PNG encoding step, and directly transfer the color data for drawing in Xojo’s canvas. I consulted GPT-4 and received [this advice 
](https://poe.com/s/zIgu9qo8VqXhpaiXvI4u). However, this solution involves setting each pixel color in C and then reading each color in Xojo to set into a Picture, which seems redundant.
Questions:
- Is it possible to set pixel colors in C and directly return the pixel data to Xojo for rendering in a Canvas?
- Are there any other suggestions or techniques for more efficiently drawing the color data processed in C onto the canvas?
I appreciate any insights or advice on how to optimize this process and improve the performance of displaying Terraria world data in the Xojo Canvas.
Thank you in advance for your help!