OSDev.org

iansjack wrote:If you don't allocate memory for the buffer you are bound to have problems. So the question you need to answer is why things don't work when you malloc() the buffer; time for a little debugging.

iansjack wrote:If you don't allocate memory for the buffer you are bound to have problems. So the question you need to answer is why things don't work when you malloc() the buffer; time for a little debugging.

ComputerFido wrote:

iansjack wrote:If you don't allocate memory for the buffer you are bound to have problems. So the question you need to answer is why things don't work when you malloc() the buffer; time for a little debugging.

Malloc is working but i am still having problems, i tried drawing a rectangle to fill the screen and it only filled about 50 pixels at the top of the screen.

Brendan wrote:Hi,

ComputerFido wrote:

iansjack wrote:If you don't allocate memory for the buffer you are bound to have problems. So the question you need to answer is why things don't work when you malloc() the buffer; time for a little debugging.

Malloc is working but i am still having problems, i tried drawing a rectangle to fill the screen and it only filled about 50 pixels at the top of the screen.

Try to figure out if it's a problem with the code that draws stuff in the double buffer, and/or if it's a problem with the code that copies the double buffer to display memory.

Looking at your old (and likely no longer relevant) code; I'd be tempted to expect multiple problems (e.g. that "fillrect()" is buggy and that "UpdateScreen()" is buggy too), but it's hard to say without seeing any of the new/relevant code.


Cheers,

Brendan

ComputerFido wrote:Looking at your old (and likely no longer relevant) code; I'd be tempted to expect multiple problems (e.g. that "fillrect()" is buggy and that "UpdateScreen()" is buggy too), but it's hard to say without seeing any of the new/relevant code.

Brendan wrote: The first problem is your handling of "pitch".

Think of the video card's display memory as rows, where each row consists of pixel data followed by none or more unused bytes (for padding). For example, for "800*600 with 32-bpp" each row might be 800*4 bytes (3200 bytes) of pixel data followed by 896 bytes of padding, that adds up to a total of 4096 bytes per row (and so "modeInfo->pitch" would be 4096).

Of course your double buffer has no padding.

Your "UpdateScreen()" assumes that there is no padding for the double buffer (correct) and that there's no padding for display memory (incorrect). This can cause pixels in the double buffer to be written to unused padding and be invisible.

void UpdateScreen(){
		for(int i=0;i<modeInfo->height;i++){
			for(int j=0;j<modeInfo->width;j++)
				screen[i*modeInfo->width*modeInfo->pitch+j] = dblBuffer[i*modeInfo->width+j];
		}
	}

ComputerFido wrote:Okay i have tried many different things to try and fix UpdateScreen() this being among them.

Code: Select all

void UpdateScreen(){
		for(int i=0;i<modeInfo->height;i++){
			for(int j=0;j<modeInfo->width;j++)
				screen[i*modeInfo->width*modeInfo->pitch+j] = dblBuffer[i*modeInfo->width+j];
		}
	}

But it still isn't working and i have no idea why. It's probably just something obvious i am missing but i am not sure. It would be really helpful if you could point me in right direction with the really annoying equation to copy the buffer

void UpdateScreen(){
		unsigned int visibleBytesPerLine = modeInfo->width * modeInfo->bpp / 8;
		uint8_t *dest = screen;
		uint8_t *src = dblBuffer;

		for(int y = 0; y < modeInfo->height; y++) {
			memcpy(dest, src, visibleBytesPerLine);
			dest += modeInfo->pitch;
			src += visibleBytesPerLine;
		}
	}