C++ :: Combine RGB (A) Pixels Into One?

I have a buffer which has a virtual width of 1024 pixels with virtual height 768 pixels (actual width stored in GPU.GPU_screenxsize, height in GPU.GPU_screenysize (both uint_32)).

I currently use the following function to plot the pixels to the screen:

inline void GPU_defaultRenderer() //Default renderer {
uint_32 pixel;
int bufferx; //Buffer's x!
int buffery; //Buffer's y!
int bufferxstart; //Buffer's x start!
int bufferystart; //Buffer's y start!
int pspx;

[Code] ...

How to combine the pixels together (blend them into one goal pixel) to get a better view? (Currently it takes the bottom right pixel of the area that represents the goal pixel).

So (x1,y1,x2,y2)->(pspx,pspy) = (bufferystart,bufferxstart,buffery,bufferx)->(pspx,pspy).
Atm this is (x2,y2)->(pspx,pspy)

Btw the pixel format is uint_32 RGBA (only RGB used atm). The psp_graphics_putpixel draws it onto the real VRAM. PSP_SCREEN_ROWS and PSP_SCREEN_COLUMNS represent the destination screen (the real screen)'s height and width in pixels.