Java | bitwise operator

Question

I've been using LWJGL for some graphics work. I am unsure how excatly the bitwise operator works. I want to mimic the OpenGL bit flags and check it with an if statement using the | bitwise operator.

I would like to reproduce this behaviorglClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

How can I use an if statement to check if GL_COLOR_BUFFER_BIT is used and another to check if GL_DEPTH_BUFFER_BIT is used.

Answer 1

Use this:

if ((myFlags & GL_COLOR_BUFFER_BIT) == GL_COLOR_BUFFER_BIT)
    // flag is set, act accordingly

Note the parens: necessary since bitwise & has a lower precedence than ==.

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Now, why this works... Let us take an hypothetical example:

public static final int TEST = 0x4;
// TEST:    0000 0000 0000 0000 0000 0000 0000 0100

value = 35;
// value:   0000 0000 0000 0000 0000 0000 0010 0011

final boolean b1 = (value & TEST) == TEST; // FALSE

value = 70;
// value:   0000 0000 0000 0000 0000 0000 0100 0110

final boolean b1 = (value & TEST) == TEST; // TRUE

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Note that in Java, such practices are generally seldomly used; you would generally prefer using an Enum instead; however, curiously there doesn't seem to be a "Do It The Java Way(tm)" API for OpenGL... All existing APIs seem to fall short of what is commonly used or, if they don't use it on purpose, do not document it :/

Answer 2

Your best bet here is to use the == relational operator seperated with parenthesis instead of the | (OR) logical operator