How to navigate memory using pointers?

CopperCircle

Hi, I am very new to C# but I am modifying an image buffer directly within memory, I am scanning along moving the pointer to get the RGB of each pixel, but I need away to jump around the image memory and read the pixels at random rather than just p++ or p--? Thanks...

  unsafe 
            { 
                byte\* p = (byte\*)(void\*)pBuffer;
                for(int y = 0; y < Height; y++)
                {
                    for(int x = 0; x < Width; x++)
                    {
                        //B
                        int srcB = p\[0\];
                        p++;
                        //G
                        int srcG = p\[0\];
                        p++;
                        //R
                        int srcR = p\[0\];
                        p++;
                    }
                }
            }

Luc Pattyn

Hi, inside an unsafe block you can use pointers and jump around as you wish, provided you tell the compiler to let you do that. What is the specific problem? :)

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Fixturized forever. :confused:

CopperCircle

Hi, the problem is I have only used Blitz Basic before and I could jump to a pixel, eg GetColor(129,280)"Width,Height", with pointers I have to scan along the image for the data, I dont know how to jump to the pixel data I want?

Guffa

For a 24 bit bitmap, the location of a pixel can be calculated with: scan0 + y * scan + x * 3 (Note that for a bitmap that is stored upside down, which is the common way, scan0 points to the last line, and scan is a negative value.) Your code for looping the image is incomplete. The lines might not be stored end-to-end in memory, you have to skip any extra bytes between the lines (calculated by scan - x * 3). Also, if the bitmap is stored upside down, you will either get the data upside down, or only getting garbage after the first line read.

Despite everything, the person most likely to be fooling you next is yourself.

Luc Pattyn

Hi, you can perform calculations with pointer values: every time you add one you move to the next element of that type (same as in C or C++). Guffa's answer below gives you a detailed example for bitmapped images. :)

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Fixturized forever. :confused: