TextRenderer.cpp

/*******************************************************************
** Taken and adapted from learnopengl.com (part of a Breakout game) 
******************************************************************/
#include <iostream>

#include <glm/gtc/matrix_transform.hpp>
#include <ft2build.h>
#include FT_FREETYPE_H

#include "text_renderer.h"
#include "resource_manager.h"


TextRenderer::TextRenderer(GLuint width, GLuint height)
{
    // Load and configure shader
    this->TextShader = ResourceManager::GetShader("text");
    this->TextShader.SetMatrix4("projection", glm::ortho(0.0f, static_cast<GLfloat>(width), static_cast<GLfloat>(height), 0.0f), GL_TRUE);
    this->TextShader.SetInteger("text", 0);
    // Configure VAO/VBO for texture quads
    glGenVertexArrays(1, &this->VAO);
    glGenBuffers(1, &this->VBO);
    glBindVertexArray(this->VAO);
    glBindBuffer(GL_ARRAY_BUFFER, this->VBO);
    glBufferData(GL_ARRAY_BUFFER, sizeof(GLfloat) * 4 * 4, NULL, GL_DYNAMIC_DRAW);
    glEnableVertexAttribArray(0);
    glVertexAttribPointer(0, 4, GL_FLOAT, GL_FALSE, 4 * sizeof(GLfloat), 0);
    glBindBuffer(GL_ARRAY_BUFFER, 0);
    glBindVertexArray(0);
}

void TextRenderer::Load(std::string font, GLuint fontSize)
{
    // First clear the previously loaded Characters
    this->Characters.clear();
    // Then initialize and load the FreeType library
    FT_Library ft;    
    if (FT_Init_FreeType(&ft)) // All functions return a value different than 0 whenever an error occurred
        std::cout << "ERROR::FREETYPE: Could not init FreeType Library" << std::endl;
    // Load font as face
    FT_Face face;
    if (FT_New_Face(ft, font.c_str(), 0, &face))
        std::cout << "ERROR::FREETYPE: Failed to load font" << std::endl;
    // Set size to load glyphs as
    FT_Set_Pixel_Sizes(face, 0, fontSize);
    // Disable byte-alignment restriction
    glPixelStorei(GL_UNPACK_ALIGNMENT, 1); 
    // Then for the first 128 ASCII characters, pre-load/compile their characters and store them
    for (GLubyte c = 0; c < 128; c++) // lol see what I did there 
    {
        // Load character glyph 
        if (FT_Load_Char(face, c, FT_LOAD_RENDER))
        {
            std::cout << "ERROR::FREETYTPE: Failed to load Glyph" << std::endl;
            continue;
        }
        // Generate texture
        GLuint texture;
        glGenTextures(1, &texture);
        glBindTexture(GL_TEXTURE_2D, texture);
        glTexImage2D(
            GL_TEXTURE_2D,
            0,
            GL_RED,
            face->glyph->bitmap.width,
            face->glyph->bitmap.rows,
            0,
            GL_RED,
            GL_UNSIGNED_BYTE,
            face->glyph->bitmap.buffer
            );
        // Set texture options
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
       
        // Now store character for later use
        Character character = {
            texture,
            glm::ivec2(face->glyph->bitmap.width, face->glyph->bitmap.rows),
            glm::ivec2(face->glyph->bitmap_left, face->glyph->bitmap_top),
            (GLuint)face->glyph->advance.x
        };
        Characters.insert(std::pair<GLchar, Character>(c, character));
    }
    glBindTexture(GL_TEXTURE_2D, 0);
    // Destroy FreeType once we're finished
    FT_Done_Face(face);
    FT_Done_FreeType(ft);
}

void TextRenderer::RenderText(StateManager &manager, std::string text, GLfloat x, GLfloat y, GLfloat scale, glm::vec3 color)
{
    manager.tex2D = NO_TEX;
    // Activate corresponding render state	
    manager.Active(this->TextShader);

    this->TextShader.SetVector3f("textColor", color);
    glActiveTexture(GL_TEXTURE0);
    glBindVertexArray(this->VAO);

    // Get the size of the whole text, to be able to center it
    glm::vec2 text_size(0);

    std::string::const_iterator c;
    for (c = text.begin(); c != text.end(); c++){
        text_size.x += (Characters[*c].Advance >> 6) * scale;
        GLint height = Characters[*c].Size.y * scale;
        text_size.y = height > text_size.y ? height : text_size.y;
    }
    text_size *= 0.5f;

    // Iterate through all characters
    for (c = text.begin(); c != text.end(); c++)
    {
        Character ch = Characters[*c];

        GLfloat xpos = x + ch.Bearing.x * scale - text_size.x;
        GLfloat ypos = y + (this->Characters['H'].Bearing.y - ch.Bearing.y) * scale - text_size.y;

        GLfloat w = ch.Size.x * scale;
        GLfloat h = ch.Size.y * scale;
        // Update VBO for each character
        GLfloat vertices[4][4] = {
            { xpos,     ypos,       0.0, 0.0 },
            { xpos,     ypos + h,   0.0, 1.0 },
            { xpos + w, ypos,       1.0, 0.0 },
            { xpos + w, ypos + h,   1.0, 1.0 }
        };
        // Render glyph texture over quad
        glBindTexture(GL_TEXTURE_2D, ch.TextureID);
        // Update content of VBO memory
        glBindBuffer(GL_ARRAY_BUFFER, this->VBO);
        glBufferSubData(GL_ARRAY_BUFFER, 0, sizeof(vertices), vertices); // Be sure to use glBufferSubData and not glBufferData

        glBindBuffer(GL_ARRAY_BUFFER, 0);
        // Render quad
        glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
        // Now advance cursors for next glyph
        x += (ch.Advance >> 6) * scale; // Bitshift by 6 to get value in pixels (1/64th times 2^6 = 64)
    }
    glBindVertexArray(0);
    glBindTexture(GL_TEXTURE_2D, 0);
}