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fusionminds

Pixel Movement?

6 posts in this topic

I''m wondering how you can clear the screen, because I''m trying to move a pixel around the screen and I need to clear the screen everytime it is moved and plots a new pixel. Can someone give me that command or help me find a new method? Thanks. - Adam Russell
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You have direct access to the video memory. There isn''t a "command", you just clear the video memory the same way you set it. Tile by tile, pixel by pixel, or by turning off the layer.

In your case, if you honestly just have one pixel or a small number of pixels, then the easiest algorithm is to just store the last location of that pixel, and every time you are about to plot the pixel in a new location, you set the old location back to whatever the background color is.

If you honestly want to clear the whole screen to erase a single pixel, then you would write your own function for clearing the screen. A loop through all the x and y coordinates that sets all the pixels to the background color.
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Or, you could use the GBA''s built-in DMA to do a much faster clear of the screen. Just create your own array that is the same size of the screen filled with what you want to clear the screen to, then just call the DMA hardware to clear the video buffer, which is much faster than doing it yourself.
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Here is my code for my pixel movement...Can you help me with it...it''s just printing lines, not moving the pixel?
-----------------------------------------------------------------
#include "gba.h" // Always the first to include
#include "keypad.h"
#include "screenmodes.h"

u16* theVideoBuffer = (u16*)VideoBuffer;
#define RGB(r,g,b) (r+(g<<5)+(b<<10)) // Macro to build a color

int main()
{
SetMode( SCREENMODE3 | BG2ENABLE );
int x = 120, y = 80;
theVideoBuffer[ x + y * 240 ] = RGB( 31, 31, 31 ); //Plot our pixel

while ( 1 )
if ( KEY_DOWN( KEYUP ) )
{
y = y + 1;
x = x;
theVideoBuffer[ x + y * 240 ] = RGB( 31, 31, 31 ); //Plot our pixel
}
else if (KEY_DOWN( KEYDOWN ) )
{
y = y - 1;
x = x;
theVideoBuffer[ x + y * 240 ] = RGB( 31, 31, 31 ); //Plot our pixel
}
else if (KEY_DOWN( KEYLEFT ) )
{
y = y - 1;
y = y;
theVideoBuffer[ x + y * 240 ] = RGB( 31, 31, 31 ); //Plot our pixel
}
else if (KEY_DOWN( KEYRIGHT ) )
{
x = x + 1;
y = y;
theVideoBuffer[ x + y * 240 ] = RGB( 31, 31, 31 ); //Plot our pixel
}
else if (KEY_DOWN( KEYSTART ) )
{
break;
}

return 0;
}
-----------------------------------------------------------------

If you can help me out then I would be so grateful...thanks.

- Adam Russell
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As msmulles said, you could clear the old pixel by setting it the the background color. That requires an extra memwrite in every if, but for only moving one pixel around, I guess that''s OK.

Another thing, I guess you ment x = x - 1 in the KEY_DOWN(KEYLEFT) if.

#include "gba.h" // Always the first to include
#include "keypad.h"
#include "screenmodes.h"

u16* theVideoBuffer = (u16*)VideoBuffer;
#define RGB(r,g,b) (r+(g<<5)+(b<<10)) // Macro to build a color

int main()
{
SetMode( SCREENMODE3 | BG2ENABLE );
int x = 120, y = 80;
theVideoBuffer[ x + y * 240 ] = RGB( 31, 31, 31 ); //Plot our pixel

while ( 1 )
if ( KEY_DOWN( KEYUP ) )
{
theVideoBuffer[ x + y * 240 ] = RGB( 0, 0, 0 ); //Plot our pixel
y = y + 1;
x = x;
theVideoBuffer[ x + y * 240 ] = RGB( 31, 31, 31 ); //Plot our pixel
}
else if (KEY_DOWN( KEYDOWN ) )
{
theVideoBuffer[ x + y * 240 ] = RGB( 0, 0, 0 ); //Plot our pixel
y = y - 1;
x = x;
theVideoBuffer[ x + y * 240 ] = RGB( 31, 31, 31 ); //Plot our pixel
}
else if (KEY_DOWN( KEYLEFT ) )
{
theVideoBuffer[ x + y * 240 ] = RGB( 0, 0, 0 ); //Plot our pixel
x = x - 1;
y = y;
theVideoBuffer[ x + y * 240 ] = RGB( 31, 31, 31 ); //Plot our pixel
}
else if (KEY_DOWN( KEYRIGHT ) )
{
theVideoBuffer[ x + y * 240 ] = RGB( 0, 0, 0 ); //Plot our pixel
x = x + 1;
y = y;
theVideoBuffer[ x + y * 240 ] = RGB( 31, 31, 31 ); //Plot our pixel
}
else if (KEY_DOWN( KEYSTART ) )
{
break;
}

return 0;
}

Good luck
-Kotumo-
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would an alternative to clearing the whole screen be to replace what was under the moving pixel/s instead?
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In the code you provided it just jumps around the place and what would I do for the mem write code? I am a newbie and not familiar with the syntax. Any help would be greatful. Thanks.

-Adam Russell
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