Question
Answer and Explanation
In the context of graphics programming or low-level manipulation of images, the term "scanline" typically refers to a single row of pixels in a bitmap image. Ending a scanline often involves moving to the next row of pixels. How you do this in C depends heavily on how you are representing and manipulating your image data.
Here are several common scenarios and methods:
1. Using a 1D Array as a Bitmap:
If your image data is stored in a 1D array, a scanline corresponds to a contiguous block of pixels. To move to the next scanline, you typically increment your pixel index by the width of the image. Here's how you might do it:
int width = 640; // Width of the image
int height = 480; // Height of the image
unsigned char pixels = malloc(width height 3); // Assuming 24-bit RGB
for (int y = 0; y < height; y++) {
for (int x = 0; x < width; x++) {
int index = (y width + x) 3; // Start of current pixel's color data
pixels[index] = 255; // Red value
pixels[index + 1] = 0; // Green value
pixels[index + 2] = 0; // Blue value
// ... pixel manipulation for single pixel here
}
// End of scanline reached, implicit move to the next scanline by loop control variable.
}
In this case, the outer for loop iterates through each row (scanline), and the inner for loop steps through each pixel within the scanline. The `y width` part effectively moves the index to the start of the next scanline.
2. Using a 2D Array (or Equivalent):
If you represent your image data using a 2D array (or a 1D array that is treated like a 2D array), then you have an explicit notion of rows. Moving to the next scanline means incrementing the row index:
int width = 640; // Width of the image
int height = 480; // Height of the image
unsigned char pixels = malloc(height sizeof(unsigned char));
for (int i = 0; i < height; i++){
pixels[i] = malloc(width 3 sizeof(unsigned char));
}
for(int y = 0; y < height; y++){
for(int x = 0; x < width; x++){
int index = x 3;
pixels[y][index] = 255; // Red value
pixels[y][index + 1] = 0; // Green value
pixels[y][index + 2] = 0; // Blue value
}
// End of scanline, next row accessed by pixels[y+1]
}
Here, each row (scanline) is accessed by the index y. The loop automatically handles the end-of-scanline by incrementing y.
3. Using Graphics Libraries:
If you're using a graphics library like SDL or OpenGL, it will typically handle the manipulation of scanlines for you when you render images. You will often not manipulate pixels directly, and will use functions or rendering pipeline to write the output on the display surface or other render target.
4. In the context of rasterization:
When rasterizing graphics primitives (lines, polygons) the scanline processing is a common algorithm. To move the next scanline means to use the next row for filling pixels. The processing usually involves an interpolation or similar procedure to fill in the pixel data.
In summary, "ending a scanline" in C most often means properly incrementing an index or variable to start at the beginning of the next row of pixels when processing bitmap images. How you implement it depends greatly on your image data structure, and how the data is accessed. The examples above provide a clearer picture.