Fastest way to draw filled quad/triangle with the SDL2 renderer?

Question

I have a game written using SDL2, and the SDL2 renderer (hardware accelerated) for drawing. Is there a trick to draw filled quads or triangles?

At the moment I'm filling them by just drawing lots of lines (SDL_Drawlines), but the performance stinks.

I don't want to go into OpenGL.

Answer 1

SDL_RenderGeometry()/SDL_RenderGeometryRaw() were added in SDL 2.0.18:

• Added SDL_RenderGeometry() and SDL_RenderGeometryRaw() to allow rendering of arbitrary shapes using the SDL 2D render API

Example:

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

int main( int argc, char** argv )
{
    SDL_Init( SDL_INIT_EVERYTHING );
    SDL_Window* window = SDL_CreateWindow("SDL", SDL_WINDOWPOS_UNDEFINED, SDL_WINDOWPOS_UNDEFINED, 800, 600, SDL_WINDOW_SHOWN );
    SDL_Renderer* renderer = SDL_CreateRenderer( window, -1, SDL_RENDERER_ACCELERATED | SDL_RENDERER_PRESENTVSYNC );

    const std::vector< SDL_Vertex > verts =
    {
        { SDL_FPoint{ 400, 150 }, SDL_Color{ 255, 0, 0, 255 }, SDL_FPoint{ 0 }, },
        { SDL_FPoint{ 200, 450 }, SDL_Color{ 0, 0, 255, 255 }, SDL_FPoint{ 0 }, },
        { SDL_FPoint{ 600, 450 }, SDL_Color{ 0, 255, 0, 255 }, SDL_FPoint{ 0 }, },
    };

    bool running = true;
    while( running )
    {
        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;
            }
        }

        SDL_SetRenderDrawColor( renderer, 0, 0, 0, SDL_ALPHA_OPAQUE );
        SDL_RenderClear( renderer );
        SDL_RenderGeometry( renderer, nullptr, verts.data(), verts.size(), nullptr, 0 );
        SDL_RenderPresent( renderer );
    }

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

    return 0;
}

Note that due to the API lacking a data channel for Z coordinates only affine texturing is achievable.

Answer 2

Not possible. SDL2 does not include a full-fledged rendering engine.

Some options:

• You could adopt Skia (the graphics library used in Chrome, among ohters) and then either stick with a software renderer, or instantiate an OpenGL context and use the hardware backend.

• You could use another 2D drawing library such as Raylib

• Or just bite the bullet and draw your triangles using OpenGL.

Answer 3

Here is my basic example:

#include <stdio.h>
#include <stdlib.h>
#include <SDL.h>

int width=1280,height=720;
SDL_Window *window = NULL;
SDL_Renderer *renderer = NULL;
SDL_Event e;

SDL_Vertex triangleVertex[3]=
{
 {
  { 0,0}, /* first point location */ 
  { 255, 0, 0, 0xFF }, /* first color */ 
  { 0.f, 0.f }
 },
 {
  { 0, 720 }, /* second point location */ 
  { 0,255,0, 0xFF }, /* second color */
  { 0.f, 0.f }
 },
 {
  { 640, 360 }, /* third point location */ 
  { 0,0,255, 0xFF }, /* third color */
  { 0.f, 0.f }
 }
};


int main(int argc, char** argv)
{
 if(SDL_Init(SDL_INIT_VIDEO)){printf( "SDL could not initialize! SDL_Error: %s\n",SDL_GetError());return -1;}

 window = SDL_CreateWindow( "SDL Chaste Triangle",SDL_WINDOWPOS_CENTERED,SDL_WINDOWPOS_CENTERED,width,height,0);
 if(window==NULL){printf( "Window could not be created! SDL_Error: %s\n", SDL_GetError() );return -1;}

 renderer = SDL_CreateRenderer(window,-1,0);
 if(renderer==NULL){printf( "Renderer could not be created! SDL_Error: %s\n", SDL_GetError() );return -1;}
    
 SDL_SetRenderDrawColor(renderer,0,0,0,255);
 SDL_RenderClear(renderer);
 if( SDL_RenderGeometry(renderer, NULL, triangleVertex, 3, NULL, 0) < 0 ) {SDL_Log("%s\n", SDL_GetError());}

 SDL_RenderPresent(renderer);
    
 while(e.type != SDL_KEYUP && e.type != SDL_QUIT) /*wait until any key is pressed and then released*/
 {
  SDL_PollEvent( &e );
 }
    
 SDL_DestroyRenderer(renderer);
 SDL_DestroyWindow(window);
 SDL_Quit();
 return 0;
}

/*
 This file is the Chastity's modification of an example from here:

 https://daywithstars.github.io/sdl2/geometry/2021/12/03/SDL2-new-geometry-rendering-SDL_RenderGeometry.html

 Unlike the original, this one is compatible with the C89 standard which Chastity always uses.

 Compile and run on Linux with this command:
 gcc -Wall -ansi -pedantic main.c -o main `sdl2-config --cflags --libs` -lm && ./main
*/

I have this one and some more examples at my github project.

https://github.com/chastitywhiterose/SDL_Chaste_Triangle

It is possible to draw any shape with enough triangles and so I made the project to help me in future games I make.