I need some help with this
BlitzPlus Forums/BlitzPlus Programming/I need some help with this
| ||
| I have a part in a game that I've been building where the character is to jump into the door to get to the another part in the game. But, when the player (HENRY) jumps into the door, I get an error message in the "MOVEMENT" variable that says "Object doesn't exist." Thus, I was wondering how do I fix my game so that I don't get that message? Here's the screenshot http://authorhenryemphrey.tripod.com/gallery/ and below is how I have my game coded. I added notes in the code so that one can go straight to where I think the problem is.
Graphics 1640, 1000
SetBuffer BackBuffer ()
timer = CreateTimer(20)
;Loading and storing the images that the game will use
HENRY = LoadAnimImage ("Move2.png",400,370,0,13)
PLATFORM = LoadImage ("Platform.png")
DOOR = LoadImage ("Door.png")
BACKGROUND = LoadImage ("BackgroundTree.jpg")
BACKGROUND2 = LoadImage ("Spaceship.jpg")
MONSTER = LoadImage ("Ball.png")
;---------------------------------------------
;Setting the Fields
Type HENRY
Field x,y
Field frame
End Type
Type BACKGROUND
Field x,y
Field image
End Type
Type PLATFORM
Field x,y
Field image
End Type
Type MONSTER
Field x,y
Field image
End Type
Type DOOR
Field x,y
Field image
End Type
;----------------------------
;Setting the original names to variables
h.HENRY = New HENRY
h\x = 500
h\y = 300
h\frame = 0
b.BACKGROUND = New BACKGROUND
b\x = 150
b\y = 150
b\image = BACKGROUND
p.PLATFORM = New PLATFORM
p\x = 200
p\y = 370
p\image = PLATFORM
m.MONSTER = New MONSTER
m\x = 600
m\y = 200
m\image = MONSTER
d.DOOR = New DOOR
d\x = 200
d\y = -200
;-----------------------------
;Miscellaneous and accessories
MOVEMENT = 1
;-----------------------------------
;the game loop
While Not KeyDown(1)
Cls
;making it so that the player appears to move right
If KeyDown(205)
b\x = b\x - 3
h\frame = h\frame + 1
If h\frame > 2 Then
h\frame = 0
EndIf
EndIf
;making it so that the player appears to move left
If KeyDown(203)
b\x = b\x + 3
h\frame = h\frame + 1
If h\frame > 12 Then
h\frame = 6
EndIf
EndIf
;this allows the player to stand on the platform
If ImagesCollide(HENRY,h\x,h\y,0,PLATFORM,(b\x + p\x),p\y,0) Then
h\y = 300
Else
h\y = h\y + 10
EndIf
;this makes the player jump
If KeyHit (57)
h\y = h\y -200
EndIf
;this makes the player come back down after jumping (maybe this is
;gravity, I think). But, maybe I need to learn how to fix this part too,
;for the player doesn't jump as eloquently as Mario on Super Mario
;Brothers
If Not KeyHit (57)
h\y = h\y + 10
EndIf
;this makes the player (Henry) appear on screen
DrawImage (HENRY,h\x,h\y,h\frame)
;this makes the platform appear on screen
DrawImage (PLATFORM,(b\x + p\x),p\y)
;here's one of the problems. This is what makes the MONSTER move backwards and forward. But when the player collides with the door,
;there's an error message that says "Object does not exist." This this is the part that I need help with.
m\x = m\x + MOVEMENT
If m\x > 800 Then MOVEMENT = -MOVEMENT
If m\x < 700 Then MOVEMENT = 1
;this makes the Monster appear on screen
DrawImage (MONSTER,(b\x + m\x),m\y)
;this is the door that the player collides with. Again, here is part of the problem. When the player collides with the door, to exit
;to exit the scene, I get an error message above in my MOVEMENT variable. The error message says "Object does not exist." Thus,
;what do I do to fix this?
If (d <> Null) Then
DrawImage (DOOR,(b\x + d\x),d\y)
If ImagesCollide (HENRY,h\x,h\y,0,DOOR,(b\x + d\x),d\y,0) Then
Delete d
Delete m
b\image = BACKGROUND2
EndIf
EndIf
Flip
Thanks |
| ||
| When you collide with the door, you delete m. So, on the next iteration of the loop, the code comes around looking for m\x and it can't find it, as it was deleted. You need to either not delete M, or make a new instance of M after you delete it. |
| ||
Sauer, after I have added the line:If (m <> Null) Then DrawImage (MONSTER,(b\x + m\x),m\y) If (d <> Null) Then DrawImage (DOOR,(b\x + d\x),d\y) If ImagesCollide (HENRY,h\x,h\y,0,DOOR,(b\x + d\x),d\y,0) Then Delete d Delete m b\image = BACKGROUND2 EndIf EndIf EndIf I still got the same message. As an experiment, I tried taking out the line where it says: m\x = m\x + MOVEMENT If m\x > 800 Then MOVEMENT = -MOVEMENT If m\x < 700 Then MOVEMENT = 1 And it worked. The monster and everything disappeared like I wanted it. But, when I added the movement back, I got that message. Thus, I wondering what do I do to stop the error message from occuring when I add movement? |
| ||
| Like Sauer said, after you have deleted m, any reference to it is meaningless, including movement. Just stick your movement code in the block that has checkes m<>NULL. |
| ||
| Yeah, you wrapped your code that has m\y in the IF check, but it's still coming to m\x later in the code and has no idea what it is. |
| ||
Thanks Sauer and John. In the bottom code block, I moved the MOVEMENT code to:
If (m <> Null) Then
m\x = m\x + MOVEMENT
If m\x > 800 Then MOVEMENT = -MOVEMENT
If m\x < 700 Then MOVEMENT = 1
DrawImage (MONSTER,(b\x + m\x),m\y)
If (d <> Null) Then
DrawImage (DOOR,(b\x + d\x),d\y)
If ImagesCollide (HENRY,h\x,h\y,0,DOOR,(b\x + d\x),d\y,0) Then
Delete m
Delete d
b\image = BACKGROUND2
EndIf
EndIf
Thus, it worked. Thanks again. |
| ||
| Glad to hear it Henry, been following your progress for a few weeks now. As a general rule, it's always best to check a 'type' exists or is valid before perfoming any checks or operations on it. These things will become second nature the more you use Blitz. Best Regards, |
| ||
| However, just to throw a spanner in the works - if you design it right from the beginning there will be no need to check if the type instance exists - just need to get the logic right.. |
| ||
| For example, it isn't always necessary to delete an instance of a type when it goes off the screen. Sometimes you just need to move it or not draw it, as to give the impression it went away. Then, when you want to use it again, your code still has all the data. Just something to think about, keep working hard. |
| ||
| Yeah, I bet older RPG games (like Earthbound) did that, that's why if you manage to get a screen away from your enemies they'll disappear and be replaced by another bunch of enemies (or none at all). |
| ||
| Good job guys on answering the main question. About your jumping problem: this might help make it a little more "eloquent"... Think about when you jump in real life. You start at a certain velocity going upwards, but gravity slows you down, and then at the apex of your jump, you begin to speed towards the ground. If you're good at math, this is a quadratic function; what you're doing now is a linear function (none of that really matters, but I thought I might add it...). So now for the code. First make a variable. Call it something like "jump" or something like that. Second add another field to the "h" type and call it "yvel" or "yvelocity". Then add the following code in place of your current jumping code.
If KeyHit(57) ;If you hit spacebar
If jump = 1 ;make sure jump = 1
h\yvel = 10 ;NOTE: change this number to make him jump higher or lower
jump = 0 ;this will prevent jumping again until he hits the ground
EndIf
EndIf
Then at the beginning of the game loop, put the following: h\y = h\y - h\vel ;this moves him up by whatever h\yvel is h\yvel = h\yvel - 1 ;NOTE: change the "1" to something else to make him rise and fall faster or slower Finally, change the ImagesCollide before the jumping code to match this:
If ImagesCollide(HENRY,h\x,h\y,0,PLATFORM,(b\x + p\x),p\y,0) Then
h\y = 300
h\yvel = 0 ;this keeps him from continually going down - ImagesCollide should take care of that, but use this just in case
jump = 1 ;this allows jumping after he returns to the ground
EndIf
And that should do it. It should be much more like Super Mario Bros. Feel free to experiment with those 2 values in the code to make the jumping more realistic. |
| ||
Caleb, I added the things that you said. In that, the character HENRY 's Jump mechanism has improved. But, I'm still trouble with him jumping in thin air if the space bar happens to be pressed twice while he's in the air. There's probably something that I didn't put in right. Below I wrote out comments on what I did and how I added things. I started the comments with ;------ as for things that I've done:
Graphics 1640, 1000
HENRY = LoadAnimImage ("Move2.png",400,370,0,13)
ENEMY = LoadImage ("MintMonster.png")
BACKGROUND = LoadImage ("DockII.jpg")
PLATFORM = LoadImage ("Big Platform2.png")
ENEMY = LoadImage ("MintMonster.png")
SetBuffer BackBuffer ()
Type HENRY
Field x,y
Field frame
Field yvel
Field vel
End Type
Type ENEMY
Field x,y
End Type
Type BACKGROUND
Field x,y
Field image
End Type
Type PLATFORM
Field x,y
Field image
End Type
;-------besides the h\x,h\y, and h\frame "h types," I added the h\yvel and h\vel (but am not sure if I did right when adding the h\vel)
h.HENRY = New HENRY
h\x = 500
h\y = 300
h\frame = 0
h\yvel = 0
h\vel =-5
e.ENEMY = New ENEMY
e\x = 800
e\y = 410
b.BACKGROUND = New BACKGROUND
b\x = 0
b\y = 700
b\image = BACKGROUND
p.PLATFORM = New PLATFORM
p\x = 100
p\y = 410
p\image = PLATFORM
;------here's the added Jump variable. I set it to "1"
Jump = 1
MOVEMENT = 1
EDMOVEMENT = 1
While Not KeyDown (1)
Cls
TileImage (b\image,b\x,b\y)
DrawImage (p\image, b\x + p\x,p\y)
DrawImage (HENRY, (b\x + h\x),h\y,h\frame)
;-----I added this section to the beginning of my game loop. Was this added correctly?
h\y = h\y - h\vel ;this moves him up by whatever h\yvel is (---this is one of the recommended sections that I added)
h\yvel = h\yvel - 1 ;NOTE: change the "1" to something else to make him rise and fall faster or slower (----this is another recommended sections that I added)
If KeyDown(205)
h\x = h\x + 3
b\x = b\x - 3 h\frame = h\frame + 1
If h\frame > 2 Then
h\frame = 0
EndIf
EndIf
If KeyDown(203)
h\x = h\x - 3
b\x = b\x + 3 h\frame = h\frame + 1
If h\frame > 12 Then
h\frame = 6
EndIf
EndIf
If KeyHit(57) ;-If you hit spacebar
h\y = h\y -200 ;-----Here's the part that I added. Maybe this part should be taken out. But, when I took it out he HENRY
;wouldn't jump. But, when this is added, if the space bar is pressed more than once, HENRY jumps in thin air.
;Thus, it seems that I should take this part out, but again HENRY won't jump at all If that was done.
If jump = 1 ;----make sure jump = 1 (this section was recommended)
h\yvel = 50 ;----NOTE: change this number to make him jump higher or lower (this section was also recommended)
jump = 0 ;----this will prevent jumping again until he hits the ground (this line was recommended as well)
EndIf
EndIf
If ImagesCollide(HENRY,h\x,h\y,0,PLATFORM,(b\x + p\x),p\y,0) Then
h\y = 430
h\yvel = 0 ;-----this keeps him from continually going down - ImagesCollide should take care of that,
;but use this just in Case
jump = 1 ;----this allows jumping after he returns to the ground
EndIf
If (e <> Null) Then
e\x = e\x + MOVEMENT
If e\x > 800 Then MOVEMENT = -MOVEMENT
If e\x < 700 Then MOVEMENT = 1
DrawImage (ENEMY,(b\x + e\x), e\y)
EndIf
Flip
Wend
|
| ||
| Sorry for taking so long to respond... I need to bookmark this thread or something... Well, for starters, I made a typo... That h\vel in the "h\y = h\y - h\vel" should be a h\yvel... Oops... That typo of mine is one of the reasons why he won't jump. The second reason is that the "ImagesCollide" part should go before the "If KeyHit(57)". The problem with it at the moment is that once h\yvel is set for how high he's gonna go, ImagesCollide() negates it because the images are already colliding, and sets it back to 0, hence why he doesn't move. The problem of doublejumping with your new "h\y = h\y - 200" (which you can get rid of now, btw) is that it raises him 200 pixels whether or not jump = 1 because it's not inside the If-then statement. Also, another thing you can change is the "h\y = 430" (it was 300 originally, wasn't it?) to an If-then statement.
If h\y > 430 ;this is in case he falls below the platform temporarily
h\y = 430 ;put him back on solid ground
EndIf
Originally, this was another thing that was causing problems with your ImagesCollide(). Once again, because the ImagesCollide() was after the Spacebar checker, it reset h\y before the changes could be made onscreen via the drawing section. Now, with this new part, he only gets reset if he falls below the platform (which can sometimes happen because of moving multiple pixels at a time). This happens so fast, though, it usually looks just like he's landing perfectly. I know this kinda sounds like a lecture (believe me, I'm falling asleep while writing it, so I fixed your code and included it below. I tested it several times to make sure it is typo and error free... lol... Hope this helps. |
| ||
| Thanks Caleb. The code worked very well. I know this kinda sounds like a lecture (believe me, I'm falling asleep while writing it, so I fixed your code and included it below. Thanks a bunch. As a person who is starting out as a beginning programmer, I appreciate all lectures lol. |
   |