190 lines
4.4 KiB
C
190 lines
4.4 KiB
C
/*
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SDL_framerate.c: framerate manager
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Copyright (C) 2001-2012 Andreas Schiffler
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This software is provided 'as-is', without any express or implied
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warranty. In no event will the authors be held liable for any damages
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arising from the use of this software.
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Permission is granted to anyone to use this software for any purpose,
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including commercial applications, and to alter it and redistribute it
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freely, subject to the following restrictions:
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1. The origin of this software must not be misrepresented; you must not
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claim that you wrote the original software. If you use this software
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in a product, an acknowledgment in the product documentation would be
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appreciated but is not required.
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2. Altered source versions must be plainly marked as such, and must not be
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misrepresented as being the original software.
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3. This notice may not be removed or altered from any source
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distribution.
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Andreas Schiffler -- aschiffler at ferzkopp dot net
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*/
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#include "SDL_framerate.h"
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/*!
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\brief Internal wrapper to SDL_GetTicks that ensures a non-zero return value.
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\return The tick count.
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*/
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Uint32 _getTicks()
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{
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Uint32 ticks = SDL_GetTicks();
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/*
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* Since baseticks!=0 is used to track initialization
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* we need to ensure that the tick count is always >0
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* since SDL_GetTicks may not have incremented yet and
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* return 0 depending on the timing of the calls.
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*/
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if (ticks == 0) {
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return 1;
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} else {
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return ticks;
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}
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}
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/*!
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\brief Initialize the framerate manager.
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Initialize the framerate manager, set default framerate of 30Hz and
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reset delay interpolation.
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\param manager Pointer to the framerate manager.
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*/
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void SDL_initFramerate(FPSmanager * manager)
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{
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/*
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* Store some sane values
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*/
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manager->framecount = 0;
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manager->rate = FPS_DEFAULT;
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manager->rateticks = (1000.0f / (float) FPS_DEFAULT);
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manager->baseticks = _getTicks();
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manager->lastticks = manager->baseticks;
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}
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/*!
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\brief Set the framerate in Hz
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Sets a new framerate for the manager and reset delay interpolation.
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Rate values must be between FPS_LOWER_LIMIT and FPS_UPPER_LIMIT inclusive to be accepted.
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\param manager Pointer to the framerate manager.
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\param rate The new framerate in Hz (frames per second).
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\return 0 for sucess and -1 for error.
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*/
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int SDL_setFramerate(FPSmanager * manager, Uint32 rate)
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{
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if ((rate >= FPS_LOWER_LIMIT) && (rate <= FPS_UPPER_LIMIT)) {
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manager->framecount = 0;
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manager->rate = rate;
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manager->rateticks = (1000.0f / (float) rate);
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return (0);
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} else {
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return (-1);
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}
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}
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/*!
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\brief Return the current target framerate in Hz
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Get the currently set framerate of the manager.
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\param manager Pointer to the framerate manager.
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\return Current framerate in Hz or -1 for error.
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*/
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int SDL_getFramerate(FPSmanager * manager)
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{
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if (manager == NULL) {
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return (-1);
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} else {
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return ((int)manager->rate);
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}
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}
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/*!
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\brief Return the current framecount.
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Get the current framecount from the framerate manager.
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A frame is counted each time SDL_framerateDelay is called.
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\param manager Pointer to the framerate manager.
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\return Current frame count or -1 for error.
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*/
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int SDL_getFramecount(FPSmanager * manager)
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{
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if (manager == NULL) {
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return (-1);
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} else {
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return ((int)manager->framecount);
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}
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}
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/*!
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\brief Delay execution to maintain a constant framerate and calculate fps.
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Generate a delay to accomodate currently set framerate. Call once in the
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graphics/rendering loop. If the computer cannot keep up with the rate (i.e.
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drawing too slow), the delay is zero and the delay interpolation is reset.
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\param manager Pointer to the framerate manager.
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\return The time that passed since the last call to the function in ms. May return 0.
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*/
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Uint32 SDL_framerateDelay(FPSmanager * manager)
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{
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Uint32 current_ticks;
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Uint32 target_ticks;
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Uint32 the_delay;
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Uint32 time_passed = 0;
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/*
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* No manager, no delay
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*/
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if (manager == NULL) {
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return 0;
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}
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/*
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* Initialize uninitialized manager
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*/
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if (manager->baseticks == 0) {
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SDL_initFramerate(manager);
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}
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/*
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* Next frame
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*/
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manager->framecount++;
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/*
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* Get/calc ticks
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*/
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current_ticks = _getTicks();
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time_passed = current_ticks - manager->lastticks;
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manager->lastticks = current_ticks;
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target_ticks = manager->baseticks + (Uint32) ((float) manager->framecount * manager->rateticks);
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if (current_ticks <= target_ticks) {
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the_delay = target_ticks - current_ticks;
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SDL_Delay(the_delay);
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} else {
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manager->framecount = 0;
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manager->baseticks = _getTicks();
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}
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return time_passed;
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}
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