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[armeggedonCounselor]

Or do something else for a bit. That worked with an earlier problem I had.

Basically, I forgot that when calling a function, you don't have to include the variable type.

There was much facepalming when I figured out what I was doing wrong.

[Stargrasper]

Anyone else here been around long enough to have used HyperCard?  What'd you think of it?  What'd you think of HyperTalk?

[DJ]

What's the standard way to display a background image in a game with a scrolling background?

I'm using SDL, and when I was learning it from a tutorial it told me to only update the part of the background where a sprite was last frame, in order to speed things up. The tutorial was using a static background, though. But I need the camera to scroll over the background as the player moves (ie background is bigger than screen area). And there's my problem - there doesn't seem to be a way to directly display just a part of the background image.

The only thing I can think of is reblitting the whole screen area every time the camera moves even one pixel, which is to say virtually every frame. I'm guessing this would be awfully slow. And yes, I know that premature optimization is a bad thing, but I just got this ugly feeling that I'm missing something super obvious here.

[Virex]

You're going to have to reblit the entire background every time the camera moves any way, there's no way around that. This is because blitting is just copying an image from video memory to the screen. What you want to avoid is loading the image into memory every time you move the camera as that is costly. SDL has options for only blitting a part of an image though. IIRC BlitSurface enables you to specify a source rectangle which indicates what part of the surface to blit, but this may depend on the language you're using.

[malloc]

The only thing I can think of is reblitting the whole screen area every time the camera moves even one pixel, which is to say virtually every frame. I'm guessing this would be awfully slow. And yes, I know that premature optimization is a bad thing, but I just got this ugly feeling that I'm missing something super obvious here.

That is pretty much the way to go. Slow? It's not too bad actually.

If you run into performance problems, it has something to do with the fact that software blitting everything to screen is generally slow. But honestly I don't think you should worry to much about hitting a bottleneck. If you do, you will probably have to which to a hardware accelerated alternative like OpenGL or DirectX, they will not have any sort of performance hit from just blitting sprites, unless you are blitting like a million of them.

[DJ]

That's what I was planning to do. Good to know I'm not doing it in a horrendously suboptimal way. I haven't actually run into any performance problems yet, but then again I only got the sprite class done so far and just tested things with one instance of it.

And yeah, I load all the graphics into a bitmap library class at startup, sprites and backgrounds just reference these images.

[Virex]

The only thing I can think of is reblitting the whole screen area every time the camera moves even one pixel, which is to say virtually every frame. I'm guessing this would be awfully slow. And yes, I know that premature optimization is a bad thing, but I just got this ugly feeling that I'm missing something super obvious here.

That is pretty much the way to go. Slow? It's not too bad actually.

If you run into performance problems, it has something to do with the fact that software blitting everything to screen is generally slow. But honestly I don't think you should worry to much about hitting a bottleneck. If you do, you will probably have to which to a hardware accelerated alternative like OpenGL or DirectX, they will not have any sort of performance hit from just blitting sprites, unless you are blitting like a million of them.

SDL can do hardware acceleration on many setups if you're in full screen mode IIRC.

[dizzyelk]

Right, so I'm trying to learn me some SDL by writing a simple RL. I'm using SDL (duh) and C++. I know C++, not an expert, but good enough. However, I'm having this weird error in one of my functions. The code is the same as with my character movement code, which works perfectly, however in this particular function it reads my keypresses twice. I fixed it by putting a SDL_WaitEvent() call at the end, but this now means that you have to hit 'Q' twice to exit. Without the SDL_WaitEvent() it'll skip 2 tiles when you hit space fr the next tile, and move 2 squares in whatever direction I press. I can't figure out what the problem is, because, as I understand it, an event is only created when a key is pressed (and, indeed, that is what happens with my movement code). Can anyone shed some light on this for me? Code after the spoiler.

Spoiler (click to show/hide)

Code: [Select]

void Map::editMap( BitmapFont disp_font, SDL_Surface * displaySurface )
{

int curX, curY, curTile; //location of the cursor and current tile

curX = 0;
curY = 0;
curTile = FLOOR_ID;

std::string cursor = "X";
std::string tilemessage;

bool stopedit = false;

tilemessage = "Current tile: ";
tilemessage += tileKey[curTile].getSym();

//fill screen with black and display the current map, cursor, info, and selected tile to place
SDL_FillRect( displaySurface, &displaySurface->clip_rect, SDL_MapRGB( displaySurface->format, 0, 0, 0 ) );
display( disp_font, displaySurface );
disp_font.show_text( curX * disp_font.get_cellW(), curY * disp_font.get_cellH(), cursor, displaySurface, YELLOW );
disp_font.show_text( 0, (WORLD_Y + 1) * disp_font.get_cellH(), "Editing map. Arrows to move, ", displaySurface, WHITE );
disp_font.show_text( (WORLD_X + 1) * disp_font.get_cellW(), 0, tilemessage, displaySurface, tileKey[curTile].getColor() );
SDL_Flip( displaySurface );

while( !stopedit )
{
//check for input
while( SDL_PollEvent( &event ) )
{
       
            if (event.type = SDL_KEYDOWN)
{
switch( event.key.keysym.sym )
{
case SDLK_KP8:
if( curY > 0 )
curY -= 1;
break;

case SDLK_KP2:
if( curY < WORLD_Y -1 )
curY += 1;
break;

case SDLK_KP4:
if( curX > 0 )
curX -= 1;
break;

case SDLK_KP6:
if( curX < WORLD_X - 1 )
curX += 1;
break;

case SDLK_KP7:
if( curX > 0 && curY > 0)
{
curX -= 1;
curY -= 1;
}
break;

case SDLK_KP9:
if( curX < WORLD_X - 1 && curY > 0 )
{
curX += 1;
curY -= 1;
}
break;

case SDLK_KP3:
if( curX < WORLD_X - 1 && curY < WORLD_Y - 1 )
{
curX += 1;
curY += 1;
}
break;

case SDLK_KP1:
if( curX > 0 && curY < WORLD_Y - 1 )
{
curX -= 1;
curY += 1;
}
break;

case SDLK_SPACE:
if( curTile < NUMTILES - 1 )
curTile += 1;
else
curTile = 0;

tilemessage = "Current tile: ";
tilemessage += tileKey[curTile].getSym();
break;

case SDLK_RETURN:
mapArray[curX][curY] = curTile;
break;

case SDLK_q:
stopedit = true;
break;

case SDLK_l:
loadMap( "map.sav" );
break;

case SDLK_s:
saveMap( "map.sav" );
break;
}

//fill screen with black and display the current map, cursor, info, and selected tile to place
SDL_FillRect( displaySurface, &displaySurface->clip_rect, SDL_MapRGB( displaySurface->format, 0, 0, 0 ) );
display( disp_font, displaySurface );
disp_font.show_text( curX * disp_font.get_cellW(), curY * disp_font.get_cellH(), cursor, displaySurface, YELLOW );
disp_font.show_text( 0, (WORLD_Y + 1) * disp_font.get_cellH(), "Editing map. NUMPAD to move, ", displaySurface, WHITE );
disp_font.show_text( (WORLD_X + 1) * disp_font.get_cellW(), 0, tilemessage, displaySurface, tileKey[curTile].getColor() );
SDL_Flip( displaySurface );

//wait for keyrelease
SDL_WaitEvent( &event );


}
        }
}
}

[Stargrasper]

Sounds like it's just reading so fast, it's reading keystrokes twice.  Try setting SDL_EnableKeyRepeat(int delay, int interval).  The api says setting delay to zero (0) will disable repeat entirely.

EDIT: It might also help to look for key release instead of key press.

[Nadaka]

I caught myself saying a moment ago while working on my work project: "This is such a hacked solution. I almost hope it doesn't work."

jasper reports are not your friend.

[dizzyelk]

Sounds like it's just reading so fast, it's reading keystrokes twice.  Try setting SDL_EnableKeyRepeat(int delay, int interval).  The api says setting delay to zero (0) will disable repeat entirely.

EDIT: It might also help to look for key release instead of key press.

I tried looking for the key release before, and also tried adding a SDL_Wait() (or whatever the syntax actually is) but they didn't help, the first acted the same, the second just made me wait between the 2 motions... looking up the SDL_EnableKeyRepeat() now...

EDIT: Nope, didn't help, its still doing it.

[RedWarrior0]

Is anyone here particularly talented in brainfuck? It looks interesting, but the name describes it very well.

[Mego]

Is anyone here particularly talented in brainfuck? It looks interesting, but the name describes it very well.

I know how the language works, but I haven't spent a whole lot of time programming in it. The most I've done is writing a C++ interpreter.

Good reference: http://esolangs.org/wiki/Brainfuck

[Aqizzar]

I had the mother of all facepalms today, debugging code with my boss.  I couldn't figure out why a page-to-print was producing growing margins with every page.  I looked that code over backwards and forwards, and then he hits a search one time, and I see the issue.

Code: [Select]

point.X = margin += colX_1;
                ^^^^ wut

Why the fuck does that even compile?  You can't set two variables in one statement, that's impossible.

[Nadaka]

I had the mother of all facepalms today, debugging code with my boss.  I couldn't figure out why a page-to-print was producing growing margins with every page.  I looked that code over backwards and forwards, and then he hits a search one time, and I see the issue.

Code: [Select]

point.X = margin += colX_1;
                ^^^^ wut

Why the fuck does that even compile?  You can't set two variables in one statement, that's impossible.

Depending on the language you can. the assignment operator is basically just another function, one that can return a value. In c, c++ and java it returns the value being set so you can do things like this:

a = b = c = d = 0;

instead of:

a = 0;
b = 0;
c = 0;
d = 0;