Direct Pixel Manipulation (looking for an example of TLN_GetBitmapPtr)

[alanhdiniz]

Hey everyone,

I've just started to learn how to use Tilengine, and I was checking ou how to do direct pixel manipulation with the TLN_GetBitmapPtr function, but when changed the value of the pointer the program segfaulted (obviously). And since I could not find any examples of that function (well, not easily at least) I decided to ask some one over here to see if I can get some help.

This is my noob code:

Code:

#include <stdio.h>
#include <stdlib.h>
#include "Tilengine.h"

int main (int argc, char* argv[])
{
   TLN_Init(400, 240, 1, 0, 0);

   TLN_SetBGColor(0, 36, 96);

   TLN_CreateWindow(NULL, 0);

   TLN_Bitmap bitmap = TLN_CreateBitmap(400, 240, 8);

   TLN_SetLayerBitmap(0, bitmap);

   int frame = 0;
   while(TLN_ProcessWindow())
   {
       TLN_DrawFrame(frame);

       for (int x = 0; x < 400; x++)
       {
           for (int y = 0; y < 240; y++)
           {
               uint8_t *pixel = TLN_GetBitmapPtr(bitmap, x, y);
               *pixel = (uint8_t)0xff;
           }
       }

       frame++;
   }

   TLN_DeleteBitmap(bitmap);
   TLN_DeleteWindow();
   TLN_Deinit();
   return 0;
}

Already thanking the support,

Alan.

[megamarc]

Hi Alan,

Welcome here and thanks for your interest!

There isn't any problem with your direct pixel manipulation code. The problem is that any layer requires having a palette assigned. When you load a bitmap with TLN_LoadBitmap() and assign it with TLN_SetLayerBitmap(), it's own palette gets loaded and attached. But you're creating an empty bitmap without a palette. Of course the renderer shouldn't crash, just refuse to draw it. I have to fix this behavior.

To fix your code, you have to manually create and assign a palette with TLN_CreatePalette() and TLN_SetBitmapPalette():

Code:

    TLN_Bitmap bitmap = TLN_CreateBitmap(400, 240, 8);
    TLN_Palette palette = TLN_CreatePalette(256);
    TLN_SetBitmapPalette(bitmap, palette);
    TLN_SetLayerBitmap(0, bitmap);

    
You should get a black window because the default palette is black. To modify it, you can use TLN_SetPaletteColor().

Let me know if it works!

[alanhdiniz]

Thanks, marc, it worked (well, at least it didn't segfaulted...),

However, I tried to use TLN_SetPaletteColor, and the background is still black. My doubt here is that if I can draw something in runtime in the bitmap layer, or I actually need to use a tileset so I can manipulate that with the bitmap layer I've created.

My current code:

Code:

#include <stdio.h>
#include <stdlib.h>
#include "Tilengine.h"

int main (int argc, char* argv[])
{
    TLN_Init(400, 240, 1, 0, 0);
    TLN_CreateWindow(NULL, CWF_VSYNC);

    TLN_Bitmap bitmap = TLN_CreateBitmap(400, 240, 8);
    TLN_Palette palette = TLN_CreatePalette(256);
    TLN_SetBitmapPalette(bitmap, palette);
    TLN_SetLayerBitmap(0, bitmap);
    TLN_SetLayerPalette(0, palette);

    for (int i = 0; i < 256; i++)
        TLN_SetPaletteColor(palette, i, 0, 36, 96);

    int frame = 0;
    int color = 0;
    while(TLN_ProcessWindow())
    {
        TLN_DrawFrame(frame);

        TLN_SetPaletteColor(palette, color, color, color, color);
        if (color < 256)
            color++;
        else color = 0;

        frame++;
    }

    TLN_DeleteBitmap(bitmap);
    // TLN_DeletePalette(palette);
    TLN_DeleteWindow();
    TLN_Deinit();
    return 0;
}

[megamarc]

Hi again!

You can -in fact you must- draw something to the bitmap you're using in order to see anything. Just setting pixels or color entries won't give any result, you must set both. Be aware that a pixel value of 0 means fully transparent.

You don't have to use tilesets: bitmap layers and tiled layers are totally independent, which one to use depends on your game needs.

In your example, your call to TLN_SetLayerPalette(0, palette); is redundant: as you've already attached the palette to the bitmap with TLN_SetBitmapPalette(), calling TLN_SetLayerBitmap() automatically sets the palette too. You can set bitmap pixels and/or palette colors at any time, the effect will be visible on the next call to TLN_DrawFrame().

Keep going!