Lazy Foo' Productions

Text Input And Clipboard Handling

Last Updated 9/14/14
Getting text input from the keyboard is a common task in games. Here we'll be getting text using SDL 2's new text input and clip board handling.
//Main loop flag bool quit = false; //Event handler SDL_Event e; //Set text color as black SDL_Color textColor = { 0, 0, 0, 0xFF }; //The current input text. std::string inputText = "Some Text"; gInputTextTexture.loadFromRenderedText( inputText.c_str(), textColor ); //Enable text input SDL_StartTextInput();
Before we go into the main loop we declare a string to hold our text and render it to a texture. We then call SDL_StartTextInput so the SDL text input functionality is enabled.
//While application is running while( !quit ) { //The rerender text flag bool renderText = false; //Handle events on queue while( SDL_PollEvent( &e ) != 0 ) {
We only want to update the input text texture when we need to so we have a flag that keeps track of whether we need to update the texture.
//Special key input else if( e.type == SDL_KEYDOWN ) { //Handle backspace if( e.key.keysym.sym == SDLK_BACKSPACE && inputText.length() > 0 ) { //lop off character inputText.pop_back(); renderText = true; } //Handle copy else if( e.key.keysym.sym == SDLK_c && SDL_GetModState() & KMOD_CTRL ) { SDL_SetClipboardText( inputText.c_str() ); } //Handle paste else if( e.key.keysym.sym == SDLK_v && SDL_GetModState() & KMOD_CTRL ) { inputText = SDL_GetClipboardText(); renderText = true; } }
There are a couple special key presses we want to handle. When the user presses back space we want to remove the last character from the string.

When the user is holding control and presses c, we want to copy the current text to the clip board using SDL_SetClipboardText. You can check if the ctrl key is being held using SDL_GetModState.

When the user does ctrl + v, we want to get the text from the clip board using SDL_GetClipboardText. Also notice that whenever we alter the contents of the string we set the text update flag.
//Special text input event else if( e.type == SDL_TEXTINPUT ) { //Not copy or pasting if( !( ( e.text.text[ 0 ] == 'c' || e.text.text[ 0 ] == 'C' ) && ( e.text.text[ 0 ] == 'v' || e.text.text[ 0 ] == 'V' ) && SDL_GetModState() & KMOD_CTRL ) ) { //Append character inputText += e.text.text; renderText = true; } } }
With text input enabled, your key presses will also generate SDL_TextInputEvents which simplifies things like shift key and caps lock. Here we first want to check that we're not getting a ctrl and c/v event because we want to ignore those since they are already handled as keydown events. If it isn't a copy or paste event, we append the character to our input string.
//Rerender text if needed if( renderText ) { //Text is not empty if( inputText != "" ) { //Render new text gInputTextTexture.loadFromRenderedText( inputText.c_str(), textColor ); } //Text is empty else { //Render space texture gInputTextTexture.loadFromRenderedText( " ", textColor ); } }
If the text render update flag has been set, we rerender the texture. One little hack we have here is if we have an empty string, we render a space because SDL_ttf will not render an empty string.
//Clear screen SDL_SetRenderDrawColor( gRenderer, 0xFF, 0xFF, 0xFF, 0xFF ); SDL_RenderClear( gRenderer ); //Render text textures gPromptTextTexture.render( ( SCREEN_WIDTH - gPromptTextTexture.getWidth() ) / 2, 0 ); gInputTextTexture.render( ( SCREEN_WIDTH - gInputTextTexture.getWidth() ) / 2, gPromptTextTexture.getHeight() ); //Update screen SDL_RenderPresent( gRenderer ); }
At the end of the main loop we render the prompt text and the input text.
//Disable text input SDL_StopTextInput();
Once we're done with text input we disable it since enabling text input introduces some overhead.
Download the media and source code for this tutorial here.

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