SDL2: Fast Pixel Manipulation

SDL_CreateTexture() w/SDL_TEXTUREACCESS_STREAMING + SDL_UpdateTexture() seems to work well enough with the right pixel format.

On my system using the default renderer:

Renderer name: direct3d
Texture formats:
SDL_PIXELFORMAT_ARGB8888
SDL_PIXELFORMAT_YV12
SDL_PIXELFORMAT_IYUV

(though the opengl info is the same:)

Renderer name: opengl
Texture formats:
SDL_PIXELFORMAT_ARGB8888
SDL_PIXELFORMAT_YV12
SDL_PIXELFORMAT_IYUV

SDL_PIXELFORMAT_ARGB8888 gives me ~1ms/frame:

// g++ main.cpp `pkg-config --cflags --libs sdl2`
#include <SDL.h>
#include <iostream>
#include <iomanip>
#include <vector>
#include <algorithm>
#include <chrono>

void UpdateFrameTiming( std::ostream& os = std::cout, float period = 2.0f )
{
    static unsigned int frames = 0;
    frames++;
    static auto start = std::chrono::steady_clock::now();
    auto end = std::chrono::steady_clock::now();

    auto seconds = std::chrono::duration< float >( end - start ).count();
    if( seconds >= period )
    {
        os
            << frames << " frames in "
            << std::setprecision( 1 ) << std::fixed << seconds << " seconds = "
            << std::setprecision( 1 ) << std::fixed << frames / seconds << " FPS ("
            << std::setprecision( 3 ) << std::fixed << seconds / frames * 1000.0 << " ms/frame)\n";
        frames = 0;
        start = end;
    }
}

int main( int, char** )
{
    SDL_Init( SDL_INIT_EVERYTHING );
    SDL_Window* window = SDL_CreateWindow( "SDL", SDL_WINDOWPOS_UNDEFINED, SDL_WINDOWPOS_UNDEFINED, 600, 600, SDL_WINDOW_SHOWN );
    SDL_Renderer* renderer = SDL_CreateRenderer( window, -1, SDL_RENDERER_ACCELERATED );
    SDL_SetHint( SDL_HINT_RENDER_SCALE_QUALITY, "1" );
    
    // dump renderer info
    SDL_RendererInfo info;
    SDL_GetRendererInfo( renderer, &info );
    std::cout << "Renderer name: " << info.name << '\n';
    std::cout << "Texture formats: " << '\n';
    for( Uint32 i = 0; i < info.num_texture_formats; i++ )
    {
        std::cout << SDL_GetPixelFormatName( info.texture_formats[i] ) << '\n';
    }

    // create texture
    const unsigned int texWidth = 1024;
    const unsigned int texHeight = 1024;
    SDL_Texture* texture = SDL_CreateTexture( renderer, SDL_PIXELFORMAT_ARGB8888, SDL_TEXTUREACCESS_STREAMING, texWidth, texHeight );
    std::vector< unsigned char > pixels( texWidth * texHeight * 4, 0 );

    bool useLocktexture = false;

    // main loop
    bool running = true;
    while( running )
    {
        SDL_SetRenderDrawColor( renderer, 0, 0, 0, SDL_ALPHA_OPAQUE );
        SDL_RenderClear( renderer );

        // handle events
        SDL_Event ev;
        while( SDL_PollEvent( &ev ) )
        {
            if( ( SDL_QUIT == ev.type ) ||
                ( SDL_KEYDOWN == ev.type && SDL_SCANCODE_ESCAPE == ev.key.keysym.scancode ) )
            {
                running = false;
                break;
            }

            if( SDL_KEYDOWN == ev.type && SDL_SCANCODE_L == ev.key.keysym.scancode )
            {
                useLocktexture = !useLocktexture;
                std::cout << "Using " << ( useLocktexture ? "SDL_LockTexture() + std::copy_n()" : "SDL_UpdateTexture()" ) << '\n';
            }
        }
        
        // splat down some random pixels
        for( unsigned int i = 0; i < 1000; i++ )
        {
            const unsigned int x = rand() % texWidth;
            const unsigned int y = rand() % texHeight;

            const unsigned int offset = ( texWidth * y * 4 ) + x * 4;
            pixels[ offset + 0 ] = rand() % 256;        // b
            pixels[ offset + 1 ] = rand() % 256;        // g
            pixels[ offset + 2 ] = rand() % 256;        // r
            pixels[ offset + 3 ] = SDL_ALPHA_OPAQUE;    // a
        }

        // update texture
        if( useLocktexture )
        {
            unsigned char* lockedPixels = nullptr;
            int pitch = 0;
            SDL_LockTexture( texture, nullptr, reinterpret_cast< void** >( &lockedPixels ), &pitch );
            std::copy_n( pixels.data(), pixels.size(), lockedPixels );
            SDL_UnlockTexture( texture );
        }
        else
        {
            SDL_UpdateTexture( texture, nullptr, pixels.data(), texWidth * 4 );
        }

        SDL_RenderCopy( renderer, texture, nullptr, nullptr );
        SDL_RenderPresent( renderer );
        
        UpdateFrameTiming();
    }

    SDL_DestroyRenderer( renderer );
    SDL_DestroyWindow( window );
    SDL_Quit();

    return 0;
}

Make sure you don’t have have vsync enabled (forced in the driver, running a compositor, etc.) or else all your frame times will be ~16ms (or whatever your display refresh is set to).