I'm running a fullscreen app with directdraw in C++. I have a function for loading maps that clears the current map and then draws all the objects for the selected map. Sometimes when a new map is loaded, 1 sprite is not drawn. As far as I can tell, it is always 1 sprite. Once this problem appears, reloading the map over and over will cause different sprites to disappear. But always 1 sprite. I'm using BltFast to draw sprites:

lpBackBuffer->BltFast(X,Y, &r, DDBLTFAST_SRCCOLORKEY | DDBLTFAST_WAIT);

I checked the errors when this problem occurs, and it is DDERR_INVALIDRECT. So I apparently have either an invalid source or destination rectangle. This is strange because there is no change in source & destination rectangles when the object is drawn correctly. I suppose this error points to a clipper issue since you can't use a clipper with BltFast, but my maps do not scroll so everything is contained within the boundaries of the screen. Pressing Alt+Tab to minimize the app and then coming back in will cause the missing object to reappear. But all I do in my restore function is reload the sprite:

sprite=DDLoadBitmap(pDD,"sprite.BMP",0,0);
DDSetColorKey(sprite, RGB(0, 0,64));

This would seem to imply that the sprite was not previously loaded correctly. If such was the case, would DDERR_INVALIDRECT be the error that shows up? I suppose I can get around the problem by reloading the bitmap whenever a DDERR_INVALIDRECT error shows up, but I would like to determine the root cause. Thanks

Thank you for your reply. I'll post what should be the relevant code.

This is an excerpt from my Load Map function that loads a Tree object from tree.bmp:




And this is an excerpt from the Draw function that draws each tree object. The count increment section does have 2 plus signs but they don't show up in my preview for some reason:



Maybe I should cast position_x[][]-bit_offset as an unsigned long instead of casting position_x[][] as an unsigned long and then subtracting bit_offset. position_x[][] is a float and bit_offset is an int. I never really paid attention to it before, but is my casting method poor here?

Also, it is inefficient to declare top_frame, bot_frame, etc for each Tree object, but that shouldn't be a problem.

If curr_frame[TREE][count] was something other than 0, an Invalid Rectangle would make sense. I am almost positive that this is not what happened, but I will make sure to verify.

Thanks

The sprites that I need in every level (like the player's character, a door, etc) are loaded when the game initializes, and all the other sprites are loaded as needed when a new map is loaded. It appears that only the level specific sprites are disappearing. The BltFast function is called at the same general location on both types of sprites, so maybe the DDLoadBitmap function is returning an error for the level specific sprites. I tried to test for the object being equal to NULL after calling DDLoadBitmap, but I didn't get any hits. Is there a list of error codes for DDLoadBitmap? I searched but had trouble finding any error checks except checking for NULL.