openglGUI.cpp

#include <openglGUI.h>
#include <ft2build.h>
#include FT_FREETYPE_H

Shader Slider::shader;
glm::mat4 Slider::orthProjection;
std::map<GLchar, Character> TextRenderer::characters;
unsigned int TextRenderer::textVAO;
unsigned int TextRenderer::textVBO;
Shader* TextRenderer::textShader;

void Slider::setup()
{
    Slider::shader.setup("shaders/vertex/shaderGui.vs", "shaders/fragment/shaderGui.fs");
    Slider::orthProjection = glm::ortho(-1.0f, 1.0f, -1.0f, 1.0f, -1.0f, 1.0f);
}

void TextRenderer::init(int scrWidth, int scrHeight)
{
    // FreeType
    // --------
    FT_Library ft;
    // All functions return a value different than 0 whenever an error occurred
    if (FT_Init_FreeType(&ft))
    {
        std::cout << "ERROR::FREETYPE: Could not init FreeType Library" << std::endl;
        exit(-1);
    }
	
	// load font as face
    FT_Face face;
    if (FT_New_Face(ft, "fonts/Arial.ttf", 0, &face)) {
        std::cout << "ERROR::FREETYPE: Failed to load font" << std::endl;
        exit(-1);
    }
    else {
        // set size to load glyphs as
        FT_Set_Pixel_Sizes(face, 0, 48);

        // disable byte-alignment restriction
        glPixelStorei(GL_UNPACK_ALIGNMENT, 1);

        // load first 128 characters of ASCII set
        for (unsigned char c = 0; c < 128; c++)
        {
            // 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
            unsigned int 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),
                face->glyph->advance.x
            };
            TextRenderer::characters.insert(std::pair<char, Character>(c, character));
        }
        glBindTexture(GL_TEXTURE_2D, 0);
    }
    // destroy FreeType once we're finished
    FT_Done_Face(face);
    FT_Done_FreeType(ft);

    // configure VAO/VBO for texture quads
    // -----------------------------------
    glGenVertexArrays(1, &TextRenderer::textVAO);
    glGenBuffers(1, &TextRenderer::textVBO);
    glBindVertexArray(TextRenderer::textVAO);
    glBindBuffer(GL_ARRAY_BUFFER, TextRenderer::textVBO);
    glBufferData(GL_ARRAY_BUFFER, sizeof(float) * 6 * 4, NULL, GL_DYNAMIC_DRAW);
    glEnableVertexAttribArray(0);
    glVertexAttribPointer(0, 4, GL_FLOAT, GL_FALSE, 4 * sizeof(float), 0);
    glBindBuffer(GL_ARRAY_BUFFER, 0);
    glBindVertexArray(0);

    TextRenderer::textShader = new Shader("shaders/vertex/text.vs", "shaders/fragment/text.fs");
    TextRenderer::updateScreen(scrWidth, scrHeight);
}

void TextRenderer::updateScreen(int scrWidth, int scrHeight)
{
    glm::mat4 projection = glm::ortho(0.0f, static_cast<float>(scrWidth), 0.0f, static_cast<float>(scrHeight));
    TextRenderer::textShader->use();
    glUniformMatrix4fv(glGetUniformLocation(TextRenderer::textShader->ID, "projection"), 1, GL_FALSE, glm::value_ptr(projection));
}

// render line of text
// -------------------
void TextRenderer::renderText(std::string text, float x, float y, float scale, glm::vec3 color)
{
    // activate corresponding render state	
    textShader->use();
    glUniform3f(glGetUniformLocation(textShader->ID, "textColor"), color.x, color.y, color.z);
    glActiveTexture(GL_TEXTURE0);
    glBindVertexArray(textVAO);

    // iterate through all characters
    std::string::const_iterator c;
    for (c = text.begin(); c != text.end(); c++) 
    {
        Character ch = this->characters[*c];

        float xpos = x + ch.Bearing.x * scale;
        float ypos = y - (ch.Size.y - ch.Bearing.y) * scale;

        float w = ch.Size.x * scale;
        float h = ch.Size.y * scale;
        // update VBO for each character
        float vertices[6][4] = {
            { xpos,     ypos + h,   0.0f, 0.0f },            
            { xpos,     ypos,       0.0f, 1.0f },
            { xpos + w, ypos,       1.0f, 1.0f },

            { xpos,     ypos + h,   0.0f, 0.0f },
            { xpos + w, ypos,       1.0f, 1.0f },
            { xpos + w, ypos + h,   1.0f, 0.0f }           
        };
        // render glyph texture over quad
        glBindTexture(GL_TEXTURE_2D, ch.TextureID);
        // update content of VBO memory
        glBindBuffer(GL_ARRAY_BUFFER, textVBO);
        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_TRIANGLES, 0, 6);
        // now advance cursors for next glyph (note that advance is number of 1/64 pixels)
        x += (ch.Advance >> 6) * scale; // bitshift by 6 to get value in pixels (2^6 = 64 (divide amount of 1/64th pixels by 64 to get amount of pixels))
    }
    glBindVertexArray(0);
    glBindTexture(GL_TEXTURE_2D, 0);
}