Garbage on top of screen when displaying text over image in devkit pro

Question

I am currently using the 16-bit libnds (Whith devkitpro) example as a basis and am trying to display text and the png background image on the same screen (in this example it is the top sceen). I am having a similar issue as this post.

I have garbage on the top of the screen (only ifconsoleInit(...) is called), similar to the first problem in the thread. The only problem is that I am displaying the background image in a different method so the fixes they made in that thread did not apply to this.

All I am looking for is whether there is a way to fix the garbage on the top of the screen. If there is a more efficient/better way to display the image, I am willing to accept it, just I haven't found a detailed enough tutorial on how to load an image as a background without using this method. Any help would be appreciated. I will answer any further questions anyone has about what is not working.

You can find the project attached here.

Answer 1

Sorry for the long delay but there are a few issues with your code. The first is that in Mode 4 the only background that can be set up as a 16 bit bitmap is layer 3. http://answers.drunkencoders.com/what-graphics-modes-does-the-ds-support/

Next, the layers all share a single chunk of background memory and your garbage is coming from you overwriting part of the bitmap in video memory with the characters for the font and the map for the console background. A simple solution is to move the bitmap by settings its map base to 1. This offsets its in graphics memory by 16KB which leaves 16KB of room for your text layer (this only works because we cant display the entire 256x256 image on screen at once due the the resolution of the DS as 256x256x2bytes fills up all of memory bank A...to be more correct we should assign another memory bank to the main background...but since we cant see the bottom 70 or so lines of pixels of our image anyway its okay that they didnt quite make it into video memory).

libnds also has a macro to make finding the memory for your background a bit simpler called "bgGetGfxPtr(id)" which will get a pointer to your background gfx in video memory after you set it up so you dont have to try to calculate it via an offset from BG_GFX.

In all the changes to your code should look like this (I added a version of this to the libnds code faq at : http://answers.drunkencoders.com/wp-admin/post.php?post=289&action=edit&message=1)

int main(void) {


    //Top screen pic init
    videoSetMode(MODE_4_2D);
    vramSetBankA(VRAM_A_MAIN_BG);
    int bg = bgInit(3, BgType_Bmp16, BgSize_B16_256x256, 1,0);
    decompress(drunkenlogoBitmap, bgGetGfxPtr(bg), LZ77Vram); //Displays/decompresses top image

    //videoSetMode(MODE_4_2D);
    consoleInit(0,0, BgType_Text4bpp, BgSize_T_256x256, 4,0, true, true);
    iprintf("\x1b[1;1HThe garbage is up here ^^^^^.");
    iprintf("\x1b[21;1HTesting the text function...");

    while(1) {
        swiWaitForVBlank();
        scanKeys();
        if (keysDown()&KEY_START) break;
    }
    return 0;
}