Raster Effect with Gendev ( SGDK)

[Stef]

Using this code it will double SOME lines but not all.I believe the reason for this is because the code is not fast enough but what could I do to make it better?

If you have H Int at each scanline your code should fit in a very small amount of cycles : we have about 488 68k cycles by scanline but the SGDK H int handler already eat a part of it (about 120 cycles) so it leave 350 cycles for your code.

You don't have to check for end of screen as H Int doesn't happen during VBlank so you can do frame initialization process in the V Int callback instead.

your H Int code can be :

Code: Select all

    *((u16 *) GFX_DATA_PORT) = vscroll;
    if (the_scroll ^= 1) vscroll--;

Then your V Int code should end by :

Code: Select all

    ...
    // re init VScroll
    vscroll=0x800; 
    // prepare H Int V Scroll writes
    *((u32 *) GFX_CTRL_PORT) = GFX_WRITE_VSRAM_ADDR(0);

[alko]

Shalom.

Please show me the complete source code of this effect (vertical scaling).

[alko]

I really need this effect

[alko]

up...

[alko]

Shalom.

Please show me the complete source code of this effect (vertical scaling).

It is even possible to implement by means of SGDK?

[ehaliewicz]

Shalom.

Please show me the complete source code of this effect (vertical scaling).

It is even possible to implement by means of SGDK?

What are you trying to do? Scaling sprites vertically?

Edit: nevermind, read the first page of the thread

[alko]

What are you trying to do? Scaling sprites vertically?

I need a raster effect - scaling planes verticaly.
https://youtu.be/RFx1XFzbICg?t=11
https://youtu.be/fpuvMCpD7_w?t=1659
https://youtu.be/CR0MWpOK1RU?t=2069
https://youtu.be/aJNEfPimU40?t=1459
https://youtu.be/OGDtViPngi8?t=148
https://youtu.be/u8TlopANMZY?t=708

[Stef]

Just use the h interrupt callback for that

Use :

Code: Select all

// Set H-Int callback
SYS_setHIntCallback(&hint_cb);
// enable H-Interrupt
VDP_setHInterrupt(1);
// set H-int line count occorence
VDP_setHIntCounter(1)

to define the hint callback method and enable H-Int for each scanline.
Then in the H-int callback you need to modify the Vertical scroll value using:

Code: Select all

void hint_cb()
{
  // modify vertical scroll
  VDP_setVerticalScroll(BPLAN, scrollValue);
}

of course you have to set a specific 'scrollValue' at each scanline to give scaling effect.

[alko]

background is flattened, but an image is unstable.

Code: Select all

....
static u32 vscrol;
void hint_cb()
{
   VDP_setVerticalScroll(PLAN_B, vscrol);
   vscrol += 8;
}

main()
{
...
while(TRUE)
{
...
SYS_setHIntCallback(&hint_cb);
VDP_setHInterrupt(1);
VDP_setHIntCounter(1);
VDP_waitVSync();   
}

}

[Stef]

Are you resetting 'vscrol' at V-Int ? looks like you aren't..

[alko]

Are you resetting 'vscrol' at V-Int ? looks like you aren't..

Oh, thanx!

Yet I keep getting flattened image.
How do stretch the picture?

[Stef]

Decrease 'vscrol' instead of increasing it =)
Using fix16 value will allow you to have smooth vertical scaling.

[danibus]

Would you be so kind to provide an example? I'm trying to strech and scroll a plane (not sprites)
I want to use a plane to show a path, like sonic 3d bonus path or similar.
This is SGDK old version.

Trying with no success

This is my code, something is missed I think, nothing happens (?)

Code: Select all

#include <genesis.h>

static u32 vscrol;
            
            void hint_cb()
            {
               VDP_setVerticalScroll(PLAN_B, vscrol);
               vscrol += 8;
            }

int main(){

    s16 id_tile_inicial = 0;
    s16 id_tile_final_planB = 0;
    s16 id_tile_final_planA = 0;

    //PLANO B
    VDP_drawImageEx(PLAN_B, &fondo_fase3B, TILE_ATTR_FULL(PAL0, FALSE, FALSE, FALSE, id_tile_inicial), 0, 0, FALSE, TRUE);
    id_tile_final_planB = id_tile_inicial + fondo_fase3B.tileset->numTile;
    //PLANO A
    VDP_drawImageEx(PLAN_A, &fondo_fase3A, TILE_ATTR_FULL(PAL0, FALSE, FALSE, FALSE, id_tile_final_planB), 0, 0, FALSE, TRUE);
    id_tile_final_planA = id_tile_final_planB + fondo_fase3A.tileset->numTile;

	while (1) {

        VDP_setScreenWidth320();
        SPR_init();

        SYS_setHIntCallback(&hint_cb);
        VDP_setHInterrupt(1);
        VDP_setHIntCounter(1);

        SPR_update();
        VDP_waitVSync();
	}

	return 0;
}

[Joe Musashi]

Here's a quick example how this can be done with SGDK 1.60.

scaling.png (16.45 KiB) Viewed 21874 times

In this example HInt and VInt look like this:

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    static u8    lineDisplay  = 0;          // line position on display screen
    static fix16 lineGraphics = 0;          // line position in graphics texture
    static fix16 scroll       = 0;          // scrolling offset
    static fix16 scale        = FIX16(4.0); // scaling factor

    void HIntHandler()
    {
        // Set line to display
        VDP_setVerticalScroll(BG_B, fix16ToInt(lineGraphics) - lineDisplay);

        // Determine next graphics line to display (+1 means image is unscaled)
        lineGraphics += scale;

        // Count raster lines
        lineDisplay++;

        // Decrease scaling factor each line
        scale -= FIX16(0.02);
    }
    void VIntHandler()
    {
        // Make sure HInt always starts with line 0
        lineDisplay = 0;

        // Reset first line we want to display
	lineGraphics = scroll;

        // Decrease scrolling offset, reset after 64 lines
	scroll = (scroll - FIX16(1)) % FIX16(64);

        // Reset scaling factor
	scale = FIX16(4.0);
 }

There are a couple of things that are important:

• We need to count the scanlines HInt is in. This is done with lineDisplay, which counts from 0 to 223, and is reset in VInt.
• lineGraphics specifies in each scanline which graphics line we want to display. If the image is not scaled, this is the same as lineDisplay. If the image size is doubled this would be lineDisplay / 2. If we want a perspective effect the scaling factor needs to be modified each line (scale variable).
• VDP_setVerticalScroll() requires a relative value, so we have to supply lineGraphics - lineDisplay to show a specific line.
• The scaling factor needs to be FIX16 so we can have values < 1 (scale = 0.5 doubles the image size).
• To achieve scrolling, the start value of lineGraphics must be altered each frame. Here we just count down 63, ... 0.

[danibus]

WoW! Nice explanation, many thanks.
Tomorrow morning I will try, still see these tricks like magic.