Lesson07: Drawing Text interactively.

Overview 

As discussed in the  previous article, we saw how Text can be drawn in multiple fonts, sizes and colors and images can be placed side by side.

Also, the implementation of the TextMesh , TextureUtil  and TextImageSketcher were covered. 

In this post we will try to draw  text and image interactively.

Details

The purpose of  Lesson07 is to draw text and image and work with them interactively by changing fonts, colors, resize height and width.

System  class diagram

The scene class does use camera. It has an pointer to TextImageSketcher called ptextutl.

Implementation

Scene

The functionality is implemented in the Scene class derived from BaseScene class.

The three methods Init, DrawScene and Cleanup are overridden as below:

The Init method calls 

1. BaseScene::Init to create hosting window and OpenGL Context. 
2. It creates an input dialog to work with text and images interactively.
3. It calls init function with texture id GL_TEXTURE0 + 4, height and width of the bitmap. on the TextImageSketcher object to populate VBO/EBO buffers and bind them. Also create texture and bitmap. 
4. It also compiles and links shader programs.

The DrawScene method draws a string and image. 

The Cleanup method releases the resources related to VBO/EBO, Texture related resources and shader programs.

The message handler for IDOK is called when Apply button is pressed after updates are made in the input dialog. It refreshes the display.

The message handler for IDCANCEL is called when in Cancel button is pressed the input dialog. It calls 

OnCloseWindow to destroy window.

Finally the WM_CLOSE  event is  handled in OnCloseWindow function and the window is destroyed and  application is shutdown when the window is closed or Escape key is pressed. 

Application

Scene class is hosted main.cpp. which creates the scene object and displays it. Message pump is added to process windows messages.

Input dialog

The input dialog as shown below can be used to change settings and understand drawing text and images.

Output

The output looks as shown in the top.