是否可以将 SDL_Texture 绘制到 OpenGL？

Question

i'm currently writing a game on SDL and I use a texture that i create in this way

SDL_Texture* target_texture = SDL_CreateTexture(ren, SDL_PIXELFORMAT_BGR555, SDL_TEXTUREACCESS_TARGET, 256, 224);

I later use

SDL_SetRenderTarget(ren, target_texture);

to make everything be drawn to this texture, everything works fine, after that I just disable the render target to texture, with

SDL_SetRenderTarget(ren, NULL);

I want to convert my game to use OpenGL for drawing stuff, and to be able to use 3D in it, but I'm running into a issue. SDL_GL_BindTexture doesn't seem to work with a SDL_Texture, My drawing code is

        SDL_Rect rect = { 32, 16, 256, 224 };
        float w = 320.f;
        float h = 240.f;
        glViewport(0, 0, w, h);
        glClearColor(0.f, 0.f, 0.f, 1.f);
        glClear(GL_COLOR_BUFFER_BIT);

        float X = float(rect.x) / float(w);
        float Y = float(rect.y) / float(h);
        float Width = float(rect.w) / float(w);
        float Height = float(rect.y) / float(h);

        //Bind the SDL_Texture in OpenGL
        SDL_GL_BindTexture(target_texture, NULL, NULL);

        //Draw the SDL_Texture * as a Quad
        glEnable(GL_TEXTURE_2D);
        glBegin(GL_QUADS); {
            glColor4f(1.0f, 1.0f, 1.0f, 1.0f);
            glTexCoord2f(0, 0); glVertex3f(X, Y, 0);
            glTexCoord2f(1, 0); glVertex3f(X + Width, Y, 0);
            glTexCoord2f(1, 1); glVertex3f(X + Width, Y + Height, 0);
            glTexCoord2f(0, 1); glVertex3f(X, Y + Height, 0);
        } glEnd();
        glDisable(GL_TEXTURE_2D);

        SDL_GL_SwapWindow(win);

This doesn't seems to work and only draws a white square to the window, which is not what i want, instead if i do this

        SDL_RenderCopy(ren, target_texture, NULL, &rect);
        SDL_RenderPresent(ren);

It works fine, but it doesn't allow me to use OpenGL at all. How do i fix this? Hopefully i explained it well enough

Example minimal reproductible code:

#include <iostream>

#include <SDL.h>
#include <SDL_opengl.h>
#include <GL/gl.h>

int main(int argc, char* argv[])
{
    SDL_Window* win = SDL_CreateWindow("test", SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED, 320, 240, SDL_WINDOW_SHOWN);
    SDL_Renderer* ren = SDL_CreateRenderer(win, 0, SDL_RENDERER_PRESENTVSYNC | SDL_RENDERER_ACCELERATED);
    SDL_Texture* target_texture = SDL_CreateTexture(ren, SDL_PIXELFORMAT_BGR555, SDL_TEXTUREACCESS_TARGET, 256, 224);
    while (true)
    {
        SDL_SetRenderTarget(ren, target_texture);

        SDL_SetRenderDrawColor(ren, 255, 0, 0, 255);


        SDL_RenderClear(ren);
        SDL_SetRenderTarget(ren, NULL);
        SDL_Rect rect = { 32, 16, 256, 224 };
        float w = 320.f;
        float h = 240.f;
        glViewport(0, 0, w, h);
        glClearColor(0.f, 0.f, 0.f, 1.f);
        glClear(GL_COLOR_BUFFER_BIT);

        float X = float(rect.x) / float(w);
        float Y = float(rect.y) / float(h);
        float Width = float(rect.w) / float(w);
        float Height = float(rect.y) / float(h);

        //Bind the SDL_Texture in OpenGL
        SDL_GL_BindTexture(target_texture, NULL, NULL);

        //Draw the SDL_Texture * as a Quad
        glEnable(GL_TEXTURE_2D);
        glBegin(GL_QUADS); {
            glColor4f(1.0f, 1.0f, 1.0f, 1.0f);
            glTexCoord2f(0, 0); glVertex3f(X, Y, 0);
            glTexCoord2f(1, 0); glVertex3f(X + Width, Y, 0);
            glTexCoord2f(1, 1); glVertex3f(X + Width, Y + Height, 0);
            glTexCoord2f(0, 1); glVertex3f(X, Y + Height, 0);
        } glEnd();
        glDisable(GL_TEXTURE_2D);

        SDL_GL_SwapWindow(win);
        SDL_Delay(16);
    }
}

Answer 1

A few issues:

• You aren't passing SDL_WINDOW_OPENGL to SDL_CreateWindow()
• You aren't creating an OpenGL context with SDL_GL_CreateContext() .
• You're trying to use an accelerated SDL_Renderer & OpenGL at the same time; there's currently no way to save/restore the GL state SDL_Renderer (might) be using to do its job

If you're dead-set on using a SDL_Renderer create one with the SDL_RENDERER_SOFTWARE flag.