framerate independent walker speed

build-web.sh

@@ -1,2 +1,2 @@
 #!/bin/bash
-/usr/lib/emscripten/em++ -std=c++26 --use-port=sdl2 -O2 --emrun --shell-file emscripten_shell.html -sASSERTIONS -o index.html main.cpp
+/usr/lib/emscripten/em++ -std=c++26 --use-port=sdl2 -O2 --shell-file emscripten_shell.html -sASSERTIONS -o index.html main.cpp

main.cpp

@@ -2,6 +2,7 @@
 
 #include <SDL2/SDL.h>
 
+#include <array>
 #include <chrono>
 #include <format>
 #include <memory>
@@ -59,11 +60,11 @@ auto operator+(SDL_Point a, SDL_Point b) {
 	return SDL_Point{.x = a.x + b.x, .y = a.y + b.y};
 }
 
+using clock = std::chrono::steady_clock;
+
 constexpr int width = 1000;
 constexpr int height = 500;
-
+constexpr auto steps_per_second = 3;
-// constexpr int width = 3440;
-// constexpr int height = 1440;
 
 template <auto EF>
 struct [[nodiscard("give this a name so SDL_Quit is called at the end"
@@ -77,8 +78,6 @@ struct [[nodiscard("give this a name so SDL_Quit is called at the end"
 	~Defer() { EF(); }
 };
 
-using clock = std::chrono::steady_clock;
-
 auto poll_events(bool& continu) {
 	for (SDL_Event e; SDL_PollEvent(&e);) {
 		if (e.type == SDL_QUIT) { continu = false; }
@@ -91,8 +90,8 @@ void mainloop(void* userData) {
 	constexpr SDL_Point directions[] = {
 		{.x = -1, .y = 0}, {.x = 1, .y = 0}, {.x = 0, .y = -1}, {.x = 0, .y = 1}
 	};
-	constexpr auto batchsize = 1000;
+	constexpr auto batchsize = 1;
-	auto& [renderer, texture, pos, pos1, rne, dist, start_time, next_poll_events_time, next_frame_render_time, frame_start, frame_time, continu] =
+	auto& [renderer, texture, pos, pos1, rne, dist, start_time, total_steps, next_poll_events_time, next_frame_render_time, frame_start, frame_time, continu] =
 		*static_cast<Loopdata*>(userData);
 
 	// measure frame_time
@@ -100,53 +99,55 @@ void mainloop(void* userData) {
 	frame_time = now - frame_start;
 	frame_start = now;
 
+	// possibly poll events
 	if (now >= next_poll_events_time) {
 		next_poll_events_time = now + std::chrono::milliseconds{200};
 		poll_events(continu);
-		std::println("last frame_time={} batchsize={}", frame_time, batchsize);
 	}
 
-	std::array<SDL_Point, batchsize> point_batch;
+	// simulate steps for passed time
-	for (auto step = 0z; step < batchsize; ++step) {
+	const auto total_time = now - start_time;
-		SDL_Point newpoint;
+	const auto target_total_steps = total_time * steps_per_second /
-		do {
+	                                clock::duration{std::chrono::seconds{1}};
-			newpoint = pos + directions[dist(rne)];
+	std::print(
-		} while (newpoint.x < 0 or newpoint.x >= width or newpoint.y < 0 or
+		"total_time={} total_steps={} target={}\r", total_time, total_steps,
-		         newpoint.y >= height);
+		target_total_steps
-		pos = newpoint;
+	);
-		point_batch[step] = newpoint;
-	}
 
-	///// Render image
+	for (; total_steps + batchsize <= target_total_steps;
-	sdl_check(SDL_SetRenderTarget(renderer, texture));
+	     total_steps += batchsize) {
-	sdl_check(SDL_SetRenderDrawBlendMode(
+		std::array<SDL_Point, batchsize> point_batch;
-		renderer,
+		for (auto step = 0z; step < batchsize; ++step) {
-		SDL_ComposeCustomBlendMode(
+			SDL_Point newpoint;
-			SDL_BLENDFACTOR_SRC_ALPHA, SDL_BLENDFACTOR_ONE_MINUS_SRC_ALPHA,
+			do {
-			SDL_BLENDOPERATION_ADD, SDL_BLENDFACTOR_ZERO, SDL_BLENDFACTOR_ONE,
+				newpoint = pos + directions[dist(rne)];
-			SDL_BLENDOPERATION_ADD
+			} while (newpoint.x < 0 or newpoint.x >= width or newpoint.y < 0 or
-		)
+			         newpoint.y >= height);
-	));
+			pos = newpoint;
-	sdl_check(SDL_SetRenderDrawColor(renderer, 0x00, 0x00, 0x00, 32));
+			point_batch[step] = newpoint;
-	sdl_check(
+		}
-		SDL_RenderDrawPoints(renderer, point_batch.data(), point_batch.size())
+
-	);
+		///// Render image
-	for (auto step = 0z; step < batchsize; ++step) {
+		sdl_check(SDL_SetRenderTarget(renderer, texture));
-		SDL_Point newpoint;
+		sdl_check(SDL_SetRenderDrawBlendMode(renderer, SDL_BLENDMODE_BLEND));
-		do {
+		sdl_check(SDL_SetRenderDrawColor(renderer, 0x00, 0x00, 0x00, 0xff));
-			newpoint = pos1 + directions[dist(rne)];
+		sdl_check(SDL_RenderDrawPoints(
-		} while (newpoint.x < 0 or newpoint.x >= width or newpoint.y < 0 or
+			renderer, point_batch.data(), point_batch.size()
-		         newpoint.y >= height);
+		));
-		pos1 = newpoint;
+		for (auto step = 0z; step < batchsize; ++step) {
-		point_batch[step] = newpoint;
+			SDL_Point newpoint;
+			do {
+				newpoint = pos1 + directions[dist(rne)];
+			} while (newpoint.x < 0 or newpoint.x >= width or newpoint.y < 0 or
+			         newpoint.y >= height);
+			pos1 = newpoint;
+			point_batch[step] = newpoint;
+		}
+		sdl_check(SDL_SetRenderDrawColor(renderer, 0xff, 0xff, 0xff, 0xff));
+		sdl_check(SDL_RenderDrawPoints(
+			renderer, point_batch.data(), point_batch.size()
+		));
 	}
-	sdl_check(SDL_SetRenderDrawColor(renderer, 0xff, 0xff, 0xff, 32));
-	sdl_check(
-		SDL_RenderDrawPoints(renderer, point_batch.data(), point_batch.size())
-	);
-	// sdl_check(SDL_SetRenderDrawColor(renderer, 0xff, 0xff, 0xff,
-	// 32)); sdl_check(SDL_RenderFillRect(renderer, nullptr));
-	// SDL_RenderCopy(renderer, fade_texture, nullptr, nullptr);
 
 	///// Render screen
 	sdl_check(SDL_SetRenderTarget(renderer, nullptr));
@@ -155,7 +156,6 @@ void mainloop(void* userData) {
 	);
 	SDL_RenderClear(renderer);
 	sdl_check(SDL_SetRenderDrawBlendMode(renderer, SDL_BLENDMODE_NONE));
-	// sdl_check(SDL_SetTextureBlendMode(texture, SDL_BLENDMODE_NONE));
 	sdl_check(SDL_RenderCopy(renderer, texture, nullptr, nullptr));
 	SDL_RenderPresent(renderer);
 }
@@ -204,9 +204,10 @@ int main() try {
 	auto next_poll_events_time = start_time;
 	auto next_frame_render_time = start_time;
 	auto frame_start = start_time;
+	auto total_steps = 0ll;
 	clock::duration frame_time;
 	auto loopdata = std::tie(
-		renderer, texture, pos, pos1, rne, dist, start_time,
+		renderer, texture, pos, pos1, rne, dist, start_time, total_steps,
 		next_poll_events_time, next_frame_render_time, frame_start, frame_time,
 		continu
 	);