Panel alpha blitting

////////////////////////////////////
/////By RyuMaster///////////////////
////////////////////////////////////



#include <acknex.h>
#include <default.c>



BMAP* original = "panel.png"; //Holder of original image
BMAP* overlayb = "overlay.png"; //Holder of our overlay image
BMAP* tempr; //This will hold original image's copy
var entered_panel = 0; //This will confirm that we create copy during overlap once



///Our image panel
PANEL* aircraft_pan =
{
bmap = original;
pos_x =200; pos_y = 200;
flags = VISIBLE;
layer = 1;
}


///Background image to see effect in real-time
PANEL* panelik =
{
bmap = "panel2.png";
layer = 0;
pos_x =0; pos_y = 0;
flags = VISIBLE;
}
///Overlay image, hidden, no VISIBLE set
PANEL* overlay =
{
bmap = overlayb;
pos_x = 800; pos_y = 400;
layer = 2;

}


function main() // start of program
{
video_mode = 8;
mouse_mode = 4;
wait(1);
level_load("");
sky_color.red = 1;
sky_color.green = 1;
sky_color.blue = 0;
video_window(NULL,NULL,0,"WaveRunner");



while(1)
{
//Attach overlay to mousy mousy
overlay.pos_x = mouse_cursor.x - overlay.size_x / 2;
overlay.pos_y = mouse_cursor.y- overlay.size_y / 2;


///Check if overlapping
if (((overlay.pos_x >= aircraft_pan.pos_x && overlay.pos_x <= aircraft_pan.pos_x + aircraft_pan.size_x) || (overlay.pos_x < aircraft_pan.pos_x && overlay.pos_x + overlay.size_x > aircraft_pan.pos_x)) && ((overlay.pos_y >= aircraft_pan.pos_y && overlay.pos_y <= aircraft_pan.pos_y + aircraft_pan.size_y) || (overlay.pos_y < aircraft_pan.pos_y && overlay.pos_y + overlay.size_y > aircraft_pan.pos_y)) )
{
/////
/////On first entry, create dublicate.
////If You use no ALPHA CHANNEL on image below, there is no need for dublicate.
////We need in order to restore correct alpha of image, when we move overlay away.
if (entered_panel == 0)
{
entered_panel = 1;
tempr = bmap_createblack(aircraft_pan.size_x, aircraft_pan.size_y,32); ///32 may be 24 if You use no alpha on source image
bmap_blit(tempr,original,NULL,NULL);
}
//Blit temp image every frame to restore correct alphas for original
bmap_blit(original, tempr, NULL, NULL);



var overlapwidth;
var overlapheight;


//Here we get all needed sizes and make sure they are OK
var squaresizex = overlay.pos_x - aircraft_pan.pos_x;
if (squaresizex >= 0)
{
overlapwidth = aircraft_pan.size_x - squaresizex - 1;
if (overlapwidth > overlay.size_x - 1)
overlapwidth = overlay.size_x - 1;
}
else
{
overlapwidth = overlay.size_x - abs(squaresizex);
if (overlapwidth > aircraft_pan.size_x - 1)
{
overlapwidth = aircraft_pan.size_x - 1;
}

}
var squaresizey = overlay.pos_y - aircraft_pan.pos_y;
if (squaresizey >= 0)
{
overlapheight = aircraft_pan.size_y - squaresizey - 1;
if (overlapheight > overlay.size_y - 1)
overlapheight = overlay.size_y - 1;
}
else
{
overlapheight = overlay.size_y - abs(squaresizey);
if (overlapheight > aircraft_pan.size_y - 1)
{
overlapheight = aircraft_pan.size_y - 1;
}

}
var squaresizex2 = aircraft_pan.pos_x - overlay.pos_x;
var squaresizey2 = aircraft_pan.pos_y - overlay.pos_y;
var format;
var pixel;
var format2;
var pixel2;


///ooooooket, let lock original and overlay
format = bmap_lock(original, 0);
format2 = bmap_lock(overlayb, 0);

if (format == 0 || format2 == 0)
error("wrong format");

var width = 0;
var height = 0;
//Process their pixel now
for (width = 0; width < overlapwidth; width++)
{
for(height = 0; height < overlapheight; height++)
{
//Here we process correct overlapping reictangle
if(squaresizex >= 0 && squaresizey >= 0)
pixel = pixel_for_bmap(overlayb,0 + width,0+height);
if(squaresizex < 0 && squaresizey >= 0)
pixel = pixel_for_bmap(overlayb,squaresizex2 + width,0+height);
if(squaresizex >= 0 && squaresizey < 0)
pixel = pixel_for_bmap(overlayb,0+ width,squaresizey2 + height);
if(squaresizex < 0 && squaresizey < 0)
pixel = pixel_for_bmap(overlayb,squaresizex2 + width,squaresizey2 + height);

COLOR tempcolor;
COLOR tempcolor2;
var putx;
var puty;
//Convert received pixel to color format
//Ok, this pixel holds transparency data
pixel_to_vec(tempcolor, NULL, format2,pixel);


var temppixel;
COLOR tempcolor2;
//Now, we take pixel from original image.
//And put our transparency data there...
if(squaresizex >= 0 && squaresizey >= 0)
{
pixel2 = pixel_for_bmap(original, squaresizex + width,squaresizey +height);
putx = squaresizex + width;
puty = squaresizey +height;
}
if(squaresizex < 0 && squaresizey >= 0)
{
pixel2 = pixel_for_bmap(original, 0 + width,squaresizey + height);
putx = 0 + width;
puty = squaresizey + height;
}
if(squaresizex >= 0 && squaresizey < 0)
{
pixel2 = pixel_for_bmap(original, squaresizex + width,0+height);
putx = squaresizex + width;
puty = 0+height;

}
if(squaresizex < 0 && squaresizey < 0)
{
pixel2 = pixel_for_bmap(original, 0 + width,0+height);
putx = 0 + width;
puty = 0 +height;

}
var alphaval;
pixel_to_vec(tempcolor2, alphaval, format,pixel2);
var newalpha = (tempcolor.blue /255) * 100; //Here we calculate new alpha from temcolor we received before
if(alphaval != 0)
{
if (alphaval < newalpha) ////This part very important. You may comment it and see why.
newalpha = alphaval;
var putpixel = pixel_for_vec(tempcolor2,newalpha,format);
pixel_to_bmap(original,putx,puty,putpixel);
}







}
}
//Unlock when all done
bmap_unlock(original);
bmap_unlock(overlayb);
}
else
{
if (entered_panel == 1)
{
//Release memory when overlay goes away...
entered_panel = 0;
bmap_blit(original, tempr, NULL, NULL);
bmap_purge(tempr);

}

}







wait(1);
}
}