Here is a nice transition. Very common effect: the second scene grows as a circle in the current scene 1 until scene 2 competely filled up the screen.
SETSCREEN 800,600,1
//#### SCENE 1 LOOP ####
WHILE KEY(57)=FALSE
// draw your stuff for scene 1 here
DRAWRECT 0,0,800,600,RGB(200,200,200)
DRAWRECT 100,100,300,300,RGB(0,0,255)
// ....
SHOWSCREEN
WEND
//#### PREPARE TRANSITION #####
CREATESCREEN 0, 7000, 800,600
USESCREEN 0
//draw your scene 1 a last time on screen 0
DRAWRECT 0,0,800,600,RGB(200,200,200)
DRAWRECT 100,100,300,300,RGB(0,0,255)
//...
USESCREEN -1
// preparing to draw a polgon ring in center of the screen with a radius (r) of 500 and an edge of 500.
// the inner radius of the ring is 0 in the beginning
LOCAL x=800/2 ; y=600/2 ; r = 500 ; edge = 500 ; col =RGB(255,255,255)
LOCAL ang
//#### START TRANSITION ####
WHILE edge > 5
// draw your stuff for scene 2 here
DRAWRECT 0,0,800,600,RGB(200,0,200)
DRAWRECT 400,400,300,300,RGB(0,255,255)
//...
edge=edge-1 // ( for fps independent speed -> for example: edge = edge- 1*DifferenceInTimeFromLastFrameToThis)
STARTPOLY 7000, 2
FOR ang = 0 TO 360 STEP 5
POLYVECTOR x+COS(ang)*r, y-SIN(ang)*r, x+COS(ang)*r, y-SIN(ang)*r,col
POLYVECTOR x+COS(ang)*(r-edge), y-SIN(ang)*(r-edge), x+COS(ang)*(r-edge),y-SIN(ang)*(r-edge),col
NEXT
ENDPOLY
SHOWSCREEN
WEND
//#### SCENE 2 LOOP ####
WHILE KEY(57)=FALSE
// draw your stuff for scene 2 here
DRAWRECT 0,0,800,600,RGB(200,0,200)
DRAWRECT 400,400,300,300,RGB(0,255,255)
//...
SHOWSCREEN
WEND
If don´t want to freeze the first scene (if it´s animated somehow) you could even redraw the screen 0 inside the transition loop.
Or just paint the ring black, close it first, then open it with the fresh scene behind. Like Looney Toons transition.
