Databases
StackOverflow2013
Postsdbo
POStrange behavior of SDL_GetKeyState()
 

Note that there are some explanatory texts on larger screens.

plurals
  1. POStrange behavior of SDL_GetKeyState()
    primarykey
    data
    text
    <p>I'm trying to write a Pong clone in C++ using SDL. Basically, I wrote a simple engine that takes care of rendering and updating</p> <pre><code>void Player::update(Uint32 ticks, SDL_Event *event, Uint8 *keys) { if(keys[SDLK_UP]) { if(m_bounds.y &gt; 0) m_bounds.y -= 2.0f * (ticks / 1000.0f); } else if(keys[SDLK_DOWN]) { if(m_bounds.y &lt; (windowInfo.getHeight() - m_bounds.h)) m_bounds.y += 2.0f * (ticks / 1000.0f); } } </code></pre> <p>The problem is that when I press the UP key, everything works like a charm, but when I press the DOWN key, it doesn't work at all. I tried everything and after a couple of hours I noticed, that when I remove the ticks and add just 2.0f it works, but I don't know why, since the conditional for the UP key looks exactly the same, except it adds, instead of substracting. I've been trying to deal with this problem a couple of hours and still have not solved it. Do you have any idea what might be wrong?</p> <p>For completeness, I'm attaching some code that calls the Player::update function, so that you know a bit more.</p> <pre><code>void Engine::update() { ++m_numOfFrames; m_elapsedTime = SDL_GetTicks() - m_startTime; while(SDL_PollEvent(&amp;m_event)) { if(m_event.type == SDL_QUIT) { m_isRunning = false; } } if(m_keys[SDLK_ESCAPE]) { m_isRunning = false; } for(Entity *entity : m_entities) { entity-&gt;update(m_elapsedTime, &amp;m_event, m_keys); } m_startTime = SDL_GetTicks(); SDL_PumpEvents(); } </code></pre> <p>EDIT: I edited the code a bit to see all the values, the code looks like this now:</p> <pre><code>if(keys[SDLK_UP]) { if(m_bounds.y &gt; 0) { m_bounds.y -= 2.0f * (ticks / 1000.0f); std::cout &lt;&lt; 2.0f * (ticks / 1000.0f) &lt;&lt; " value of Y:" &lt;&lt; m_bounds.y &lt;&lt; std::endl; } } else if(keys[SDLK_DOWN]) { if(m_bounds.y &lt; (windowInfo.getHeight() - m_bounds.h)) { m_bounds.y += 2.0f * (ticks / 1000.0f); std::cout &lt;&lt; 2.0f * (ticks / 1000.0f) &lt;&lt; " value of Y:" &lt;&lt; m_bounds.y &lt;&lt; std::endl; } } </code></pre> <p>The result in console are pretty much the same for both, except for the DOWN conditional, the value of <code>m_bounds.y</code> doesn't change at all, it's always the same, although it's been added a line higher. The error must be on this line:</p> <pre><code>m_bounds.y += 2.0f * (ticks / 1000.0f); </code></pre>
    singulars
    1. PO
      singulars
      1. PTAnswer
    1. This table or related slice is empty.
    1. PTQuestion
    1. USgenpfault
    1. USmichy04
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. PO
      singulars
      1. PTAnswer
    1. This table or related slice is empty.
    1. COI would guess both _Up_ and _Down_ are pressed at the same time, at least to the program... How do you fill up your `m_keys`?
      singulars
      1. POStrange behavior of SDL_GetKeyState()
      1. USK-ballo
    2. COI do fill m_keys with this code `m_keys = SDL_GetKeyState(0);` And not, they are not pressed at the same time, I tried lots of pressing variations and nothing changed.
      singulars
      1. POStrange behavior of SDL_GetKeyState()
      1. USmichy04
    3. COInsufficient debug output in your `Player::update` function. There's loads more investigation can be done
      singulars
      1. POStrange behavior of SDL_GetKeyState()
      1. USLightness Races in Orbit
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload