Alpha channel have no effect when drawn to texture and pasted to window

Using SDL2, I want to draw some graphics on texture and paste it on window for speed enhancement. When I paste it I want my alpha channel preserved.

This code is supposed to show a white rotating transparent rectangle.

But it shows opaque white rectangle.

How can I get a transparent white rectangle?

#ifdef __linux__
#include <SDL2/SDL.h>
#elif defined(_WIN32)
#include <SDL.h>
#endif

const int WIN_WIDTH = 640;
const int WIN_HEIGHT = 480;

int main(int argc, char **argv){
	if (SDL_Init(SDL_INIT_EVERYTHING) != 0){
		std::cerr << "SDL_Init failed: " << SDL_GetError() << "\n";
		return 1;
	}
	SDL_Window *win = SDL_CreateWindow("Rendering to a texture!", SDL_WINDOWPOS_CENTERED,
		SDL_WINDOWPOS_CENTERED, WIN_WIDTH, WIN_HEIGHT, SDL_WINDOW_SHOWN | SDL_WINDOW_ALLOW_HIGHDPI);

	SDL_Renderer *renderer = SDL_CreateRenderer(win, -1,
		SDL_RENDERER_ACCELERATED | SDL_RENDERER_TARGETTEXTURE);

	//Put your own bmp image here
	SDL_SetRenderDrawBlendMode(renderer, SDL_BLENDMODE_BLEND);

	//Make a target texture to render too
	SDL_Texture *texTarget = SDL_CreateTexture(renderer, SDL_PIXELFORMAT_RGBA8888,
		SDL_TEXTUREACCESS_TARGET, WIN_WIDTH, WIN_HEIGHT);
	
	//Now render to the texture
	SDL_SetRenderTarget(renderer, texTarget);
	SDL_SetRenderDrawColor(renderer, 255, 255, 255, 100);
	SDL_RenderClear(renderer);
	//Detach the texture
	SDL_SetRenderTarget(renderer, NULL);
	SDL_SetRenderDrawColor(renderer, 255, 0, 0, 0);
	SDL_RenderClear(renderer);

	//Now render the texture target to our screen, but upside down
	for(int i=0; i<255; i++) {
		SDL_RenderClear(renderer);
		SDL_RenderCopyEx(renderer, texTarget, NULL, NULL, i, NULL, SDL_FLIP_VERTICAL);
		SDL_RenderPresent(renderer);

		SDL_Delay(10);
	}

	SDL_DestroyTexture(texTarget);
	SDL_DestroyRenderer(renderer);
	SDL_DestroyWindow(win);
	SDL_Quit();
	return 0;
}

Use SDL_SetTextureBlendMode on the texture, not SDL_SetRenderDrawBlendMode.

SDL_SetTextureBlendMode(texTarget, SDL_BLENDMODE_BLEND);

The wiki for SDL_SetRenderDrawBlendMode says:

> Set the blend mode used for drawing operations (Fill and Line).

Drawing operations are SDL_RenderDrawLine and such.

On the other hand, SDL_RenderCopy says:

> The texture is blended with the destination based on its blend mode set with SDL_SetTextureBlendMode().