How to control device context in two ways

SDL Development
1

Code:

#include “sdl\SDL.h”

SDL_Texture* Image1;
SDL_Rect I1;
SDL_Surface* Image2;
SDL_Rect I2;

int testshow = 1;
int wmain()
{
SDL_Window* pWindow = NULL;
SDL_Renderer* pRenderer = NULL;
SDL_Surface* screen = NULL;

SDL_Init(SDL_INIT_EVERYTHING);
pWindow = SDL_CreateWindow(u8"????????????", SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED, 1920, 1080, SDL_WINDOW_SHOWN | SDL_WINDOW_ALLOW_HIGHDPI);

pRenderer = SDL_CreateRenderer(pWindow, -1, 0);
screen = SDL_GetWindowSurface(pWindow);

//read 1.bmp 300x300 bgr
char ImageBuffer[300 * 300 * 3];
FILE* infile;
_wfopen_s(&infile, L"1.bmp", L"rb");
fseek(infile, 54, SEEK_SET);
fread(ImageBuffer, sizeof(ImageBuffer), 1, infile);
fclose(infile);
SDL_Surface* buffer = SDL_CreateRGBSurfaceFrom(ImageBuffer, 300, 300, 3 * 8, 300 * 3, 0x0000FF, 0x00FF00, 0xFF0000, 0x000000);
Image1 = SDL_CreateTextureFromSurface(pRenderer, buffer);
I1.x = I1.y = 20;I1.w = I1.h = 300;

//read 2.bmp 300x300 bgr
_wfopen_s(&infile, L"2.bmp", L"rb");
fseek(infile, 54, SEEK_SET);
fread(ImageBuffer, sizeof(ImageBuffer), 1, infile);
fclose(infile);
Image2 = SDL_CreateRGBSurfaceFrom(ImageBuffer, 300, 300, 3 * 8, 300 * 3, 0x0000FF, 0x00FF00, 0xFF0000, 0x000000);
I2.x = 350;I2.y = 20;I2.w = I2.h = 300;

SDL_Event event;
bool sQuit = false;
while (!sQuit) 
{
	while (SDL_PollEvent(&event))
	{
		switch (event.type)
		{
		case SDL_KEYDOWN:
			if (event.key.keysym.sym == SDLK_ESCAPE) 
			{
				sQuit = true;
			}
			if (event.key.keysym.sym == SDLK_1)
			{
				testshow = 1;
			}
			if (event.key.keysym.sym == SDLK_2) 
			{
				testshow = 2;
			}
			break;
		case SDL_QUIT:
			sQuit = true;
			break;
		default:
			break;
		}
	}
	
	//SDL_RenderClear(pRenderer);
	SDL_RenderCopy(pRenderer, Image1, NULL, &I1);//video card memory data
	SDL_BlitSurface(Image2, NULL, screen, &I2);//random access memory data

	//I want two methods for image render, but output image will flickering. could have only one.
	SDL_RenderPresent(pRenderer);//video card render mode
	SDL_UpdateWindowSurface(pWindow);//random access memory render mode

	/*
	switch (testshow)
	{
	case 1:
		SDL_RenderClear(pRenderer);
		SDL_RenderCopy(pRenderer, Image1, NULL, &I1);
		SDL_RenderPresent(pRenderer);
		break;
	case 2:
		SDL_BlitSurface(Image2, NULL, screen, &I2);
		SDL_UpdateWindowSurface(pWindow);
		break;
	}
	*/
}
SDL_Quit();

}

I want “SDL_RenderPresent” and “SDL_UpdateWindowSurface” in the same screen.
For example, ???SDL_Texture??? is normal image, ???SDL_Surface??? is Chinese characters. about render font, render ???SDL_Surface???,Instead of from ???SDL_Surface??? to ???SDL_Texture???.

2

Hello.

You can use SDL_SetRenderTarget to draw/prepare everything first on a texture.

eg:

  1. Rendering a sentence “Hello World”
  2. Use SDL_SetRenderTarget to draw each character on a texture.
  3. Use SDL_RenderCopy to “present” it many times/game loop without recreating the sentence.
  4. SDL_RenderPresent to draw everything.------------------------
    http://digitalspine.blogspot.com
3

Thanks~~
but… not in English.
Only 26 letters in English.
I use Chinese characters, cannot allocate all temporary render texture.

Demo:
1.Read *.txt file.
2.Set sdl_ttf sdk (set read *.ttf file)
3.Chinese characters to SDL_Surface.
4.SDL_Surface to SDL_Texture.
5.Render image texture and font texture.

I have done this before. but now i want cancel the step 4.