int red = sha << 16;
int green = sha<< 8;
int blue = sha;
color -= (red | green | blue);
Shading an RGB value
Author
Hello All,
I'm trying to shade and rgb value by a value
What Zipster said.
You could write a color class, which implements a subtraction operator (that is, if you are on c++, otherwise you would write a function "subtract()"), which internally does subtraction on three seperate values. Or if you rely on all components being in a single value, you have to decompose it first (using shifts and bitand's).
Upon subtraction, the easiest way is to convert each component into a signed integer of a bigger bitsize, perform a subtraction, clamp it to an upper/lower limit, and cast it back into the components/the color value.
You could write a color class, which implements a subtraction operator (that is, if you are on c++, otherwise you would write a function "subtract()"), which internally does subtraction on three seperate values. Or if you rely on all components being in a single value, you have to decompose it first (using shifts and bitand's).
Upon subtraction, the easiest way is to convert each component into a signed integer of a bigger bitsize, perform a subtraction, clamp it to an upper/lower limit, and cast it back into the components/the color value.
Author
I'm not writing in OO i'm afraid. Is there a nice clean way to extract the RGB elements and clamp them to zero?
Bitwise ops, just revert what you have already used:
First, a struct could be handy:
Then, to get the components:
Now we are going to define a clamp function:
Next, an example function to add colors (which will use the clamping function):
At last, you can use your three rgb values and shift up what you need:
Code is in plain C. Not tested.
// your codeint red = sha << 16;int green = sha << 8;int blue = sha;First, a struct could be handy:
// r,g,b are supposef to represent value between 0 and 0xFF.// We have declared them as integers in order to take "over/under-flow"// into account.struct RGB { int r, g, b;};Then, to get the components:
assert (sizeof (int) > 1); // But you can bet on that.// How we would decompose:RGB rgb = { (sha >> 16) & 0xFF, // The value 0xFF is 11111111 in binary, (sha >> 8) & 0xFF, // and with the bitand we filter out every bit sha & 0xFF // that is on the "left" side};Now we are going to define a clamp function:
void clamp (RGB *rgb) { assert (0 != rgb); if (rgb->r < 0) rgb->r = 0; else if (rgb->r > 0xFF) rgb->r = 0xFF; if (rgb->g < 0) rgb->g = 0; else if (rgb->g > 0xFF) rgb->g = 0xFF; if (rgb->b < 0) rgb->b = 0; else if (rgb->b > 0xFF) rgb->b = 0xFF;}Next, an example function to add colors (which will use the clamping function):
void clamp (RGB *target, const RGB *lhs, const RGB *rhs) { assert (0 != target && 0 != lhs && 0 != rhs); target->r = lhs->r + rhs->r; target->g = lhs->g + rhs->g; target->b = lhs->b + rhs->b; clamp (target);}At last, you can use your three rgb values and shift up what you need:
RGB alpha, bravo, charlie;...add (&alpha, &bravo, &charlie);uint32_t final = (alpha.r << 16) | (alpha.g << 8) | alpha.b;Code is in plain C. Not tested.
Author
Thanks for that, it was really really help full.
I modified one of the functions because I don't really need so many stucts lying around.
Thanks again :)
I modified one of the functions because I don't really need so many stucts lying around.
void clamp (RGB *lhs, const int shade) { lhs->r += shade; lhs->g += shade; lhs->b += shade; clamp (lhs);}Thanks again :)
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