需要帮助更正使用sdl2设置像素的算法

Question

我正试图使用SDL2编写一个setPixel函数，但此代码无法按预期工作。

根据这个函数的需要，我有窗口、渲染器和纹理指针作为全局变量。

#include <SDL2/SDL.h>
#include <iostream>
using namespace std;
SDL_Window* window = NULL;
SDL_Renderer* renderer = NULL;
SDL_Texture* texture = NULL;
bool running = false;

void handleEvents();
void update();
void render();
void setPixel(int x, int y, Uint8 r, Uint8 g, Uint8 b);
int main(int argc, char const *argv[])
{

if (SDL_Init(SDL_INIT_EVERYTHING) != 0)
{
cout << "SDL init failed " << SDL_GetError() << "n";
return 1;
}

window = SDL_CreateWindow("Testing_01",
SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED, 
800, 640, 
SDL_WINDOW_SHOWN);
if (window == NULL)
{
cout << "Window creation failed " << SDL_GetError() << "n";
return 1;
}
renderer = SDL_CreateRenderer(window, -1, 0);
if (renderer == NULL)
{
cout << "Renderer creation failed " << SDL_GetError() << "n";
return 1;
}
SDL_SetRenderDrawColor(renderer, 230, 230, 230, 255);
setPixel(10, 10, 255, 0, 0);
running = true;
while (running)
{
handleEvents();
update();
render();
}
SDL_DestroyTexture(texture);
SDL_DestroyRenderer(renderer);
SDL_DestroyWindow(window);
SDL_Quit();
return 0;
}
void handleEvents()
{   
SDL_Event event;
const Uint8 *keys = SDL_GetKeyboardState(NULL);
while (SDL_PollEvent(&event))
{
switch (event.type)
{
case SDL_QUIT:
running = false;
break;
default:
break;
}
}
if (keys[SDL_SCANCODE_ESCAPE]) 
{
running = false;
}
if (keys[SDL_SCANCODE_RIGHT]) 
{
printf("Right and Up Keys Pressed.n");
}
}
void update()
{
}

void render()
{
SDL_RenderClear(renderer);
SDL_RenderPresent(renderer);
}
void setPixel(int x, int y, Uint8 r, Uint8 g, Uint8 b)
{   
// Allocate memory for a pixel buffer.
Uint32 *pixels = new Uint32[800 * 640];
// Clear the pixel buffer.
memset(pixels, 0, 800 * 640 * sizeof(Uint32));
SDL_Rect rect, bound;
rect.x = 0;
rect.y = 0;
rect.w = 800;
rect.h = 640;
bound = rect;
const SDL_Rect* constRect = &rect;
Uint32 color;
texture = SDL_CreateTexture(renderer,
SDL_PIXELFORMAT_RGB888,
SDL_TEXTUREACCESS_STREAMING, 800,
640);

SDL_LockTexture(texture,
constRect,
(void**) pixels, (int*)( 800 * sizeof(Uint32)));
color = SDL_MapRGB(SDL_AllocFormat(SDL_PIXELFORMAT_RGBA8888), r, g, b);
pixels[(y*800)+x] = color;
SDL_UpdateTexture(texture,
constRect,
pixels, 800 * sizeof(Uint32));
delete[] pixels;
SDL_RenderCopy(renderer, texture, &rect, &bound);
SDL_UnlockTexture(texture);
}

Answer 1

您可以将SDL_RenderDrawPoint与SDL_SetSendDrawColor结合使用，以实现您想要的效果(假设您只是想直接在屏幕上绘制像素(。这种方法不需要使用中间纹理来绘制。

我已将您的设置像素功能更改为：

void setPixel(int x, int y, Uint8 r, Uint8 g, Uint8 b) {
SDL_SetRenderDrawColor(renderer, r, g, b, SDL_ALPHA_OPAQUE);
SDL_RenderDrawPoint(renderer, x, y);
}

和您的渲染函数：

void render()
{
SDL_SetRenderDrawColor(renderer, 230, 230, 230, 255);
SDL_RenderClear(renderer);
setPixel(10, 10, 255, 0, 0);
SDL_RenderPresent(renderer);
}

像素将在每次更新时用我提供的样本重新绘制。

您可以查看此相关问题以了解更多信息。

Answer 2

欢迎使用SDL2！

你不应该锁定纹理，如果你要写在上面。