Problem with getting a background bitmap to persist in a sprite shooting game.

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Geoff

17

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Joined: 10th Jul 2007

Location: Sheffield (U.K.)

Posted: 29th Apr 2011 19:06

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I am in the first stage of building this game.

My current problem:-
In the code below, you will see that, in order to prevent the background image flickering or disappearing, I have had to include the statement "Paste Image back, 0, 0" in three places:-
In the Do/Loop, and twice more in the "fireBullet()" function.

Is there a better way to achieve this, please?
I would also welcome any other guidance on my present code as far as it goes.

Thank you, Geoff.

(It will be apparent from the first 5 globals that I am using a bitmap background, and 4 sprites.)

Hide Mouse

Global back As Integer = 1
Global plane As Integer = 2
Global missile As Integer = 3
Global ufo As Integer = 4
Global explode As Integer = 5

Global ang As Word
Global ufoX As Float
Global ufoY As Float
Global ufoXamt As Float
Global ufoYamt As Float
Global explosionX As Float
Global explosionY As Float

loadGraphics()

Do
Paste Image back, 0, 0 `needed
checkInput()
handleUfo()
testCollisions()
Loop

Function loadGraphics()
Load Image "Space.bmp",back `**I thought only this one was needed.

Load Image "Ship.bmp",plane
Sprite plane,400,550,plane
OffSet Sprite plane,32,32

Load Image "Ufo.bmp",ufo
Sprite ufo,900,750,ufo

Load Image "Missile.bmp",missile
Sprite missile,900,800,missile
OffSet Sprite missile,12,5

Load Image "Explode.bmp",explode
Sprite explode,900,850,explode

EndFunction

Function handleUfo()
ufoY = 50
ufoXamt = 2
ufoX = ufoX + ufoXamt
If ufoX > 800 Then ufoX = 0
Sprite ufo,ufoX,ufoY,ufo
EndFunction

Function checkInput()
If SpaceKey()
fireBullet()
EndIf

EndFunction

Function fireBullet()
x = 408
y = 550
Repeat
handleUfo()
Paste Image back, 0, 0 `*****needed
y = y - 15
Sprite missile,x,y,missile
testCollisions()
Until y < -15
Paste Image back, 0, 0 `*****needed
EndFunction

Function testCollisions()
If Sprite Collision(missile,ufo)
Hide Sprite ufo
Hide Sprite missile
Sprite explode,ufoX,ufoY,explode
EndIf
EndFunction

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KISTech

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Joined: 8th Feb 2008

Location: Aloha, Oregon

Posted: 29th Apr 2011 21:16

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Texture a plane with it, position the plane in the proper place in front of the camera to represent the background.

If you have to move the background along with player movement use SCROLL OBJECT TEXTURE and scroll it in the desired direction.

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Geoff

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Joined: 10th Jul 2007

Location: Sheffield (U.K.)

Posted: 29th Apr 2011 23:36

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Thank you KISTech, for your quick response.
I seem to be out of my depth here. I suspect that your suggestions relate to 3D programming. I should have made it clearer that I haven't got very far with "2"D yet.
The program I'm trying to build is very loosely based on J S Harbour's "Astro Gunner" (His book:- "Dark Basic Pro Game Programming, 2nd edn.").
In that 2D program, he pastes the background image only once (at the top of the main game loop), and the background is stable all the time.

If I run my program with only one "Paste Image back, 0, 0" in the Do/Loop, whenever the player presses the space bar to fire a missile, the background disappears completely.

Does this help to describe my problem?
Geoff.

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Hodgey

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Joined: 10th Oct 2009

Location: Australia

Posted: 30th Apr 2011 01:36 Edited at: 30th Apr 2011 01:39

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I think you're missing a "sync on" and a "sync rate 60" at the beginning of your program. You will also need a "sync" in your loop right at the end, like this

+ Code Snippet

sync on : sync rate 60
do
   // code here

   sync
loop

Oh and please post your code in snippets like this [ code]yourcode[ /code] without the spaces in the code tags.

A clever person solves a problem, a wise person avoids it - Albert Einstein

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Rich Dersheimer

AGK Developer

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Joined: 1st Jul 2009

Location: Inside the box

Posted: 30th Apr 2011 05:44 Edited at: 30th Apr 2011 05:45

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Two thoughts...

Use the TEXTURE BACKDROP command to add a background to your game.

Here is an example:

+ Code Snippet

set display mode 640,480,32
for nStar = 1 to 1000
    dot rnd(640),rnd(480),rgb(255,255,255)
next nStar

get image 1,0,0,640,480
cls 0
box 0,0,64,64
get image 2,0,0,64,64

texture backdrop 1

do
    for x = -64 to 640
        sprite 1,x,240,2
        wait 1
    next x
    for x = 640 to -64 step -1
        sprite 1,x,240,2
        wait 1
    next x
loop

Use the SET SPRITE command to stop the sprite from erasing the pasted backdrop.

Here's an example:

+ Code Snippet

set display mode 640,480,32
for nStar = 1 to 1000
    dot rnd(640),rnd(480),rgb(255,255,255)
next nStar

get image 1,0,0,640,480
cls 0
box 0,0,64,64
get image 2,0,0,64,64

paste image 1,0,0
set sprite 1,1,1

do
    for x = -64 to 640
        sprite 1,x,240,2
        wait 1
    next x
    for x = 640 to -64 step -1
        sprite 1,x,240,2
        wait 1
    next x
loop

Either method works without re-pasting the background in your main loop.

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Geoff

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Joined: 10th Jul 2007

Location: Sheffield (U.K.)

Posted: 30th Apr 2011 18:58

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Thank you Hodgey,
I have tried your suggestion to use Sync statements, and the background does stay in place while the user presses the space bar, but unfortunately, the ufo and missile images do not show at all.
I am sure that this will be caused by my poor coding in the rest of the program.

Thank you Rich,
Your first suggestion gives the error message:- "This command is now obsolete". (I am using DB pro version 1.055).
Your second suggestion works fine, and I like with the starry background it produces.

But my Space.bmp was obviously artist produced, and I would like to get it to behave itself. My present plan is to continue studying J.S.Harbour's program.

All help will be gratefully received. Geoff.

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Rich Dersheimer

AGK Developer

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Joined: 1st Jul 2009

Location: Inside the box

Posted: 30th Apr 2011 21:31 Edited at: 30th Apr 2011 21:58

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Quote: "This command is now obsolete"

Yes, it was taken out for a while, but is back in now, with the newer versions.

EDIT: If you would post your media, we could all check the code. Aside from that, I'll check with "alternative" media.

This code works, but it uses alternative media. As Hodgey suggests, including sync commands makes sure you show your sprites when you want them to be seen.

Hide Mouse
set display mode 800,600,32
sync on
sync rate 72

Global back As Integer = 1
Global plane As Integer = 2
Global missile As Integer = 3
Global ufo As Integer = 4
Global explode As Integer = 5

Global ang As Word
Global ufoX As Float
Global ufoY As Float
Global ufoXamt As Float
Global ufoYamt As Float
Global explosionX As Float
Global explosionY As Float

loadGraphics()
paste image back,0,0
set sprite plane,1,1

Do
    checkInput()
    handleUfo()
    testCollisions()
    sync
Loop

Function loadGraphics()
`Load Image "Space.bmp",back
for nStar = 1 to 1000
    dot rnd(800),rnd(600),rgb(255,255,255)
next nStar
get image back,0,0,800,600

`Load Image "Ship.bmp",plane
cls 0
box 0,0,64,64
get image plane,0,0,64,64
Sprite plane,400,550,plane
OffSet Sprite plane,32,32

`Load Image "Ufo.bmp",ufo
ink rgb(0,0,255),0
box 0,0,64,64
get image ufo,0,0,64,64
Sprite ufo,900,750,ufo

`Load Image "Missile.bmp",missile
cls 0
ink rgb(255,255,0),0
box 0,0,24,10
get image missile,0,0,24,10
Sprite missile,900,800,missile
OffSet Sprite missile,12,5

`Load Image "Explode.bmp",explode
cls 0
ink rgb(255,0,0),0
box 0,0,64,64
get image explode,0,0,64,64
cls 0
Sprite explode,900,850,explode 
EndFunction

Function handleUfo()
ufoY = 50
ufoXamt = 2
ufoX = ufoX + ufoXamt
If ufoX > 800 Then ufoX = 0
Sprite ufo,ufoX,ufoY,ufo
sync
EndFunction

Function checkInput()
If SpaceKey()
    fireBullet()
EndIf
EndFunction

Function fireBullet()
x = 408
y = 550
Repeat
     handleUfo()
     y = y - 15
     Sprite missile,x,y,missile
     sync
     testCollisions()
Until y < -15
EndFunction

Function testCollisions()
If Sprite Collision(missile,ufo)
     Hide Sprite ufo
     Hide Sprite missile
     Sprite explode,ufoX,ufoY,explode
     sync
EndIf
EndFunction

+ Code Snippet

Hide Mouse
set display mode 800,600,32
sync on
sync rate 72

Global back As Integer = 1
Global plane As Integer = 2
Global missile As Integer = 3
Global ufo As Integer = 4
Global explode As Integer = 5

Global ang As Word
Global ufoX As Float
Global ufoY As Float
Global ufoXamt As Float
Global ufoYamt As Float
Global explosionX As Float
Global explosionY As Float

loadGraphics()
paste image back,0,0
set sprite plane,1,1

Do
    checkInput()
    handleUfo()
    testCollisions()
    sync
Loop

Function loadGraphics()
`Load Image "Space.bmp",back
for nStar = 1 to 1000
    dot rnd(800),rnd(600),rgb(255,255,255)
next nStar
get image back,0,0,800,600

`Load Image "Ship.bmp",plane
cls 0
box 0,0,64,64
get image plane,0,0,64,64
Sprite plane,400,550,plane
OffSet Sprite plane,32,32

`Load Image "Ufo.bmp",ufo
ink rgb(0,0,255),0
box 0,0,64,64
get image ufo,0,0,64,64
Sprite ufo,900,750,ufo

`Load Image "Missile.bmp",missile
cls 0
ink rgb(255,255,0),0
box 0,0,24,10
get image missile,0,0,24,10
Sprite missile,900,800,missile
OffSet Sprite missile,12,5

`Load Image "Explode.bmp",explode
cls 0
ink rgb(255,0,0),0
box 0,0,64,64
get image explode,0,0,64,64
cls 0
Sprite explode,900,850,explode 
EndFunction

Function handleUfo()
ufoY = 50
ufoXamt = 2
ufoX = ufoX + ufoXamt
If ufoX > 800 Then ufoX = 0
Sprite ufo,ufoX,ufoY,ufo
sync
EndFunction

Function checkInput()
If SpaceKey()
    fireBullet()
EndIf
EndFunction

Function fireBullet()
x = 408
y = 550
Repeat
     handleUfo()
     y = y - 15
     Sprite missile,x,y,missile
     sync
     testCollisions()
Until y < -15
EndFunction

Function testCollisions()
If Sprite Collision(missile,ufo)
     Hide Sprite ufo
     Hide Sprite missile
     Sprite explode,ufoX,ufoY,explode
     sync
EndIf
EndFunction

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Geoff

17

Years of Service

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Joined: 10th Jul 2007

Location: Sheffield (U.K.)

Posted: 6th May 2011 23:12

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Thank you, Rich, for your help.
I have managed to get my 5 .bmp's to work, by substituting them for your temporary graphic methods.

I shall now enjoy developing my program from a sound start.

Thank you all, Geoff

P.S. I couldn't discover how to post my .bmp's, but I don't expect anyone will be waiting anxiously to see them.
If anyone is, please let me know how to post them.

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