I want a bullet to move when I click Space. First the bullet image is blitted when space is pressed, at the same time a timer starts and when it reaches 5000 ms ticks the x-value of the image should change. This is my code:
SDL_Rect bulletRect;
bulletRect.x = dstX+31; //dstX/Y is the source destination of another image where the bullet should be drawn
bulletRect.y = dstY+10.5;
SDL_Surface *bullet = IMG_Load(bullet.png");
if (drawBullet) //bool set to true in the space key event.
{
SDL_BlitSurface(bullet, NULL, screen, &bulletRect);
//timer
my_timer.start(); //starts the timer
if (SDL_GetTicks() == 5000) //if 5 sec
{
bulletRect.x += 10;
}
}
The image is only blitted but nothing happens after 5 sec. What is wrong?
Your conditional statement
if (SDL_GetTicks() == 5000) //if 5 sec
{
bulletRect.x += 10;
}
is inside the statement
if (drawBullet) //bool set to true in the space key event
which means you only check the timer once when the spacebar is pressed. Move this outside the if(drawBullet)
You should have SDL_GetTicks() >= 5000, instead of checking for ==5000, otherwise you'll only enter the condition if you happen to hit 5000 by pure luck.
from SDL's documentation, SDL_GetTicks function: Returns the number of milliseconds since SDL library initialization. This value wraps around if the program runs for more than 49.7 days
so if you're checking that it's been 5 seconds since it moved last (not sure what else you could be trying to do here) you want to store the current number of ticks and use that to compare against during the next loop (check that the difference between previous and current is > 5000)
Related
I'm learning SDL and I have a frustrating problem. Code is below.
Even though there is a loop that keeps the program alive, when I load an image and change the x value of the source rect to animate, the image that was loaded disappears after exactly 15 seconds. This does not happen with static images. Only with animations. I'm sure there is a simple thing I'm missing but I cant see it.
void update(){
rect1.x = 62 * int ( (SDL_GetTicks() / 100) % 12);
/* 62 is the width of a frame, 12 is the number of frames */
}
void shark(){
surface = IMG_Load("s1.png");
if (surface != 0){
texture = SDL_CreateTextureFromSurface(renderer,surface);
SDL_FreeSurface(surface);
}
rect1.y = 0;
rect1.h = 90;
rect1.w = 60;
rect2.x = 0;
rect2.y = 0;
rect2.h = rect1.h+30; // enlarging the image
rect2.w = rect1.w+30;
SDL_RenderCopy(renderer,texture,&rect1,&rect2);
}
void render(){
SDL_SetRenderDrawColor(renderer, 0, 0, 100, 150);
SDL_RenderPresent(renderer);
SDL_RenderClear(renderer);
}
and in main
update();
shark();
render();
SDL_image header is included, linked, dll exists. Could be the dll is broken?
I left out rest of the program to keep it simple. If this is not enough, I can post the whole thing.
Every time you call the shark function, it loads another copy of the texture. With that in a loop like you have it, you will run out of video memory quickly (unless you are calling SDL_DestroyTexture after every frame, which you have not indicated). At which point, you will no longer be able to load textures. Apparently this takes about fifteen seconds for you.
If you're going to use the same image over and over, then just load it once, before your main loop.
This line int ( (SDL_GetTicks() / 100) % 12);
SDL_GetTicks() returns the number of miliseconds that have elapsed since the lib initialized (https://wiki.libsdl.org/SDL_GetTicks). So you're updating with the TOTAL AMOUNT OF TIME since your application started, not the time since last frame.
You're supposed to keep count of the last time and update the application with how much time has passed since the last update.
Uint32 currentTime=SDL_GetTicks();
int deltaTime = (int)( currentTime-lastTime );
lastTime=currentTime; //declared previously
update( deltaTime );
shark();
render();
Edit: Benjamin is right, the update line works fine.
Still using the deltaTime is a good advice. In a game, for instance, you won't use the total time since the beginning of the application, you'll probably need to keep your own counter of how much time has passed (since you start an animation).
But there's nothing wrong with that line for your program anyhow.
I have managed to create a system that allows game objects to move according to the change in time (rather than the change in number of frames). I am now, for practise's sake, trying to impose a FPS limiter.
The problem I'm having is that double the amount of game loops are occurring than what I expect. For example, if I try to limit the number of frames to 1 FPS, 2 frames will pass in that one second - one very long frame (~1 second) and 1 extremely short frame (~15 milliseconds). This can be shown by outputting the difference in time (in milliseconds) between each game loop - an example output might be 993, 17, 993, 16...
I have tried changing the code such that delta time is calculated before the FPS is limited, but to no avail.
Timer class:
#include "Timer.h"
#include <SDL.h>
Timer::Timer(void)
{
_currentTicks = 0;
_previousTicks = 0;
_deltaTicks = 0;
_numberOfLoops = 0;
}
void Timer::LoopStart()
{
//Store the previous and current number of ticks and calculate the
//difference. If this is the first loop, then no time has passed (thus
//previous ticks == current ticks).
if (_numberOfLoops == 0)
_previousTicks = SDL_GetTicks();
else
_previousTicks = _currentTicks;
_currentTicks = SDL_GetTicks();
//Calculate the difference in time.
_deltaTicks = _currentTicks - _previousTicks;
//Increment the number of loops.
_numberOfLoops++;
}
void Timer::LimitFPS(int targetFps)
{
//If the framerate is too high, compute the amount of delay needed and
//delay.
if (_deltaTicks < (unsigned)(1000 / targetFps))
SDL_Delay((unsigned)(1000 / targetFps) - _deltaTicks);
}
(Part of the) game loop:
//The timer object.
Timer* _timer = new Timer();
//Start the game loop and continue.
while (true)
{
//Restart the timer.
_timer->LoopStart();
//Game logic omitted
//Limit the frames per second.
_timer->LimitFPS(1);
}
Note: I am calculating the FPS using a SMA; this code has been omitted.
The problem is part of how your timer structure is setup.
_deltaTicks = _currentTicks - _previousTicks;
I looked though the code a few times and based on how you have the timer setup this seems to be the problem line.
Walking though it at the start of your code _currentTicks will equal 0 and _previousTicks will equal 0 so for the first loop your _deltaTicks will be 0. This means regardless of your game logic LimitFPS will misbehave.
void Timer::LimitFPS(int targetFps)
{
if (_deltaTicks < (unsigned)(1000 / targetFps))
SDL_Delay((unsigned)(1000 / targetFps) - _deltaTicks);
}
We just calculated that _deltaTicks was 0 at the start of the loop, thus we wait the full 1000ms regardless of what happens in your game logic.
On the next frame we have this, _previousTicks will equal 0 and _currentTicks will now equal approximately 1000ms. This means the _deltaTicks will be equal to 1000.
Again we hit the LimitFPS function but this time with a _deltaTicks of 1000 which makes it so we wait for 0ms.
This behavior will constantly flip like this.
wait 1000ms
wait 0ms
wait 1000ms
wait 0ms
...
those wait 0ms essentially double your FPS.
You need to test for time at the start and end of your game logic.
//The timer object.
Timer* _timer = new Timer();
//Start the game loop and continue.
while (true)
{
//Restart the timer.
_timer->LoopStart();
//Game logic omitted
//Obtain the end time
_timer->LoopEnd();
//Now you can calculate the delta based on your start and end times.
_timer->CaculateDelta();
//Limit the frames per second.
_timer->LimitFPS(1);
}
Hope that helps.
Assuming your gameloop is triggered only when SDL_Delay() expired wouldn't it be enough to write:
void Timer::LimitFPS(int targetFps)
{
SDL_Delay((unsigned)(1000 / targetFps));
}
to delay your gameloop by the right amount of milliseconds depending on the requested target FPS?
I am attempting to insert a delay in Processing sketch. I tried Thread.sleep() but I guess it will not work because, as in Java, it prevents rendering of the drawings.
Basically, I have to draw a triangle with delays in drawing three sides.
How do I do that?
Processing programs can read the value of computer’s clock. The current second is read with the second() function, which returns values from 0 to 59. The current minute is read with the minute() function, which also returns values from 0 to 59. - Processing: A Programming Handbook
Other clock related functions : millis(), day(), month(), year().
Those numbers can be used to trigger events and calculate the passage of time, as in the following Processing sketch quoted from the aforementioned book:
// Uses millis() to start a line in motion three seconds
// after the program starts
int x = 0;
void setup() {
size(100, 100);
}
void draw() {
if (millis() > 3000) {
x++;
line(x, 0, x, 100);
}
}
Here's an example of a triangle whose sides are drawn each one after 3 seconds (the triangle is reset every minute):
int i = second();
void draw () {
background(255);
beginShape();
if (second()-i>=3) {
vertex(50,0);
vertex(99,99);
}
if (second()-i>=6) vertex(0,99);
if (second()-i>=9) vertex(50,0);
endShape();
}
As #user2468700 suggests, use a time keeping function. I like millis().
If you have a value to keep track of the time at certain intervals and the current time (continuously updated) you can check if one timer(manually updated one) falls behind the other(continuous one) based on a delay/wait value. If it does, update your data (number of points to draw in this case) and finally the local stop-watch like value.
Here's a basic commented example.
Rendering is separated from data updates to make it easier to understand.
//render related
PVector[] points = new PVector[]{new PVector(10,10),//a list of points
new PVector(90,10),
new PVector(90,90)};
int pointsToDraw = 0;//the number of points to draw on the screen
//time keeping related
int now;//keeps track of time only when we update, not continuously
int wait = 1000;//a delay value to check against
void setup(){
now = millis();//update the 'stop-watch'
}
void draw(){
//update
if(millis()-now >= wait){//if the difference between the last 'stop-watch' update and the current time in millis is greater than the wait time
if(pointsToDraw < points.length) pointsToDraw++;//if there are points to render, increment that
now = millis();//update the 'stop-watch'
}
//render
background(255);
beginShape();
for(int i = 0 ; i < pointsToDraw; i++) {
vertex(points[i].x,points[i].y);
}
endShape(CLOSE);
}
I'm making my first game in allegro 5, it's a snake game. In order to move the snake game I'd want to use a squared grid which I made, so the snake moves at regular intervals.
How can I use timers to make an event happen at a certain amount of time?
For example, I want my snake to move every second in the direction set, I know how to control him but I don't know how to create an event which happens at a certain interval. I'm using Codeblocks IDE with Windows XP SP3
Most people who create games with Allegro used a fixed interval timing system. This means X times per second (often 60 or 100), you process input and run a logic cycle. Then, if you have time left over, you draw a frame of graphics.
To create a timer that ticks at 60 FPS and register it with an event queue:
ALLEGRO_TIMER *timer = al_create_timer(1 / 60.0);
ALLEGRO_EVENT_QUEUE *queue = al_create_event_queue();
al_register_event_source(queue, al_get_timer_event_source(timer));
Now somewhere in your main event loop:
al_start_timer(timer);
while (playingGame)
{
bool draw_gfx = false;
do
{
ALLEGRO_EVENT event;
al_wait_for_event(queue, &event);
if (event.type == ALLEGRO_EVENT_TIMER)
{
do_logic();
draw_gfx = true;
}
else if (event.type == ... )
{
// process keyboard input, mouse input, whatever
// this could change the direction the snake is facing
}
}
while (!al_is_event_queue_empty(queue));
if (draw_gfx)
{
do_gfx();
draw_gfx = false;
}
}
So now in do_logic(), you can move your snake one unit in the direction it is facing. This means it would move 60 units per second. You can use fractional units if you need more granularity.
You may want to take a look at some of the demos that come with Allegro, as they have full featured event loops. It's too much to include as a single SO answer.
I am aware of the MoveWindow() and SetWindowPos() functions. I know how to use them correctly. However, what I am trying to accomplish is move a window slowly and smoothly as if a user is dragging it.
I have yet to get this to work correctly. What I tried was getting the current coordinates with GetWindowRect() and then using the setwindow and movewindow functions, incrementing Right by 10 pixels each call.
Any ideas?
Here is what I had beside all my definitions.
while(1)
{
GetWindowRect(notepad,&window);
Sleep(1000);
SetWindowPos(
notepad,
HWND_TOPMOST,
window.top - 10,
window.right,
400,
400,
TRUE
);
}
If you want smooth animation, you'll need to make it time-based, and allow Windows to process messages in between movements. Set a timer, and respond to WM_TIMER notifications by moving the window a distance based on the elapsed time since your animation started. For natural-looking movement, don't use a linear function for determining the distance - instead, try something like Robert Harvey's suggested function.
Pseudocode:
//
// animate as a function of time - could use something else, but time is nice.
lengthInMS = 10*1000; // ten second animation length
StartAnimation(desiredPos)
{
originalPos = GetWindowPos();
startTime = GetTickCount();
// omitted: hwnd, ID - you'll call SetTimer differently
// based on whether or not you have a window of your own
timerID = SetTimer(30, callback);
}
callback()
{
elapsed = GetTickCount()-startTime;
if ( elapsed >= lengthInMS )
{
// done - move to destination and stop animation timer.
MoveWindow(desiredPos);
KillTimer(timerID);
}
// convert elapsed time into a value between 0 and 1
pos = elapsed / lengthInMS;
// use Harvey's function to provide smooth movement between original
// and desired position
newPos.x = originalPos.x*(1-SmoothMoveELX(pos))
+ desiredPos.x*SmoothMoveELX(pos);
newPos.y = originalPos.y*(1-SmoothMoveELX(pos))
+ desiredPos.y*SmoothMoveELX(pos);
MoveWindow(newPos);
}
I found this code which should do what you want. It's in c#, but you should be able to adapt it:
increment a variable between 0 and 1 (lets call it "inc" and make it global) using small increments (.03?) and use the function below to give a smooth motion.
Math goes like this:
currentx=x1*(1-smoothmmoveELX(inc)) + x2*smoothmmoveELX(inc)
currenty=y1*(1-smoothmmoveELX(inc)) + y2*smoothmmoveELX(inc)
Code:
public double SmoothMoveELX(double x)
{
double PI = Atn(1) * 4;
return (Cos((1 - x) * PI) + 1) / 2;
}
http://www.vbforums.com/showthread.php?t=568889
A naturally-moving window would accelerate as it started moving, and decelerate as it stopped. The speed vs. time graph would look like a bell curve, or maybe the top of a triangle wave. The triangle wave would be easier to implement.
As you move the box, you need to steadily increase the number of pixels you are moving the box each time through the loop, until you reach the halfway point between point a and point b, at which you will steadily decrease the number of pixels you are moving the box by. There is no special math involved; it is just addition and subtraction.
If you are bored enough, you can do loopback VNC to drag the mouse yourself.
Now, as for why you would want to I don't know.