The Four Keys

When selecting someone, they select for talent not simple experience, intellengence or determination.

When setting expectation, they define the right outcomes not the right steps.

When motivating someone, they focus on strengths not on weaknesses.

When developing someone, they help them to find the right fit not the next rung on the promotion ladder.

来自 “ ITPUB博客 ” ,链接:http://blog.itpub.net/27028038/viewspace-733127/,如需转载,请注明出处,否则将追究法律责任。

转载于:http://blog.itpub.net/27028038/viewspace-733127/

Now, we have a way to perceive that the user is pressing a key. We know when we want to move up, down, left, and right. We know at each iteration of the main loop exactly, what the user wants; we just have to update the circle with a new position depending on this input. This method gives us a great advantage. So finally we can write something in our update() function, namely, the movement of our player. We check which of the four Boolean member variables is true, and determine the movement accordingly. By using += (instead of =) and if (instead of else if), we implicitly handle the case where two opposite keys, such as right and left are pressed at the same time—the movement stays zero. The update() function is shown in the following code snippet: void Game::update() { sf::Vector2f movement(0.f, 0.f); if (mIsMovingUp) movement.y -= 1.f; if (mIsMovingDown) movement.y += 1.f; if (mIsMovingLeft) movement.x -= 1.f; if (mIsMovingRight) movement.x += 1.f; mPlayer.move(movement); } We introduce two new things here: a vector and the move() function on the circle shape. The move() function does what its name says, it moves the shape by the amount we provide it. Vector algebra Vectors are an important part of algebraic mathematics. They imply lots of rules and definitions, which go beyond the scope of our book. However, SFML's sf::Vector2 class template is way more practical, both in concept and functionality. To be as simple as we could possibly be, we know that a coordinate in a two-dimensional Cartesian system would need two components: x and y. Because in graphics all coordinates are expressed with the decimal float data type, sf::Vector2 is instantiated as sf::Vector2<float>, which conveniently has a typedef named sf::Vector2f. Such an object is made to contain two member variables, x and y. This makes our life simpler, because now we don't need to pass two variables to functions, as we can fit both in a single sf::Vector2f object. sf::Vector2f also defines common vector operations, such as additions and subtractions with other vectors, or multiplications and divisions with scalars (single values), effectively shortening our code.翻译,要求每行中英文对照
03-08
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