221 lines
6.7 KiB
C++
221 lines
6.7 KiB
C++
#include <stdio.h>
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#include <stdlib.h>
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#include <math.h>
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#include <GL/glew.h>
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#include <GL/freeglut.h>
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#define GLM_FORCE_RADIANS
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#include <glm/glm.hpp>
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#include <glm/gtc/matrix_transform.hpp>
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#include <glm/gtc/type_ptr.hpp>
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#include <ft2build.h>
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#include FT_FREETYPE_H
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#include "common/shader_utils.h"
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GLuint program;
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GLint attribute_coord;
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GLint uniform_tex;
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GLint uniform_color;
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struct point {
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GLfloat x;
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GLfloat y;
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GLfloat s;
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GLfloat t;
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};
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GLuint vbo;
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FT_Library ft;
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FT_Face face;
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const char *fontfilename;
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int init_resources() {
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/* Initialize the FreeType2 library */
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if (FT_Init_FreeType(&ft)) {
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fprintf(stderr, "Could not init freetype library\n");
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return 0;
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}
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/* Load a font */
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if (FT_New_Face(ft, fontfilename, 0, &face)) {
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fprintf(stderr, "Could not open font %s\n", fontfilename);
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return 0;
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}
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program = create_program("text.v.glsl", "text.f.glsl");
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if(program == 0)
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return 0;
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attribute_coord = get_attrib(program, "coord");
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uniform_tex = get_uniform(program, "tex");
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uniform_color = get_uniform(program, "color");
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if(attribute_coord == -1 || uniform_tex == -1 || uniform_color == -1)
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return 0;
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// Create the vertex buffer object
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glGenBuffers(1, &vbo);
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return 1;
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}
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/**
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* Render text using the currently loaded font and currently set font size.
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* Rendering starts at coordinates (x, y), z is always 0.
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* The pixel coordinates that the FreeType2 library uses are scaled by (sx, sy).
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*/
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void render_text(const char *text, float x, float y, float sx, float sy) {
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const char *p;
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FT_GlyphSlot g = face->glyph;
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/* Create a texture that will be used to hold one "glyph" */
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GLuint tex;
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glActiveTexture(GL_TEXTURE0);
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glGenTextures(1, &tex);
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glBindTexture(GL_TEXTURE_2D, tex);
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glUniform1i(uniform_tex, 0);
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/* We require 1 byte alignment when uploading texture data */
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glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
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/* Clamping to edges is important to prevent artifacts when scaling */
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glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
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glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
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/* Linear filtering usually looks best for text */
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glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
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glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
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/* Set up the VBO for our vertex data */
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glEnableVertexAttribArray(attribute_coord);
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glBindBuffer(GL_ARRAY_BUFFER, vbo);
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glVertexAttribPointer(attribute_coord, 4, GL_FLOAT, GL_FALSE, 0, 0);
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/* Loop through all characters */
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for (p = text; *p; p++) {
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/* Try to load and render the character */
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if (FT_Load_Char(face, *p, FT_LOAD_RENDER))
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continue;
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/* Upload the "bitmap", which contains an 8-bit grayscale image, as an alpha texture */
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glTexImage2D(GL_TEXTURE_2D, 0, GL_ALPHA, g->bitmap.width, g->bitmap.rows, 0, GL_ALPHA, GL_UNSIGNED_BYTE, g->bitmap.buffer);
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/* Calculate the vertex and texture coordinates */
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float x2 = x + g->bitmap_left * sx;
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float y2 = -y - g->bitmap_top * sy;
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float w = g->bitmap.width * sx;
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float h = g->bitmap.rows * sy;
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point box[4] = {
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{x2, -y2, 0, 0},
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{x2 + w, -y2, 1, 0},
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{x2, -y2 - h, 0, 1},
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{x2 + w, -y2 - h, 1, 1},
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};
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/* Draw the character on the screen */
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glBufferData(GL_ARRAY_BUFFER, sizeof box, box, GL_DYNAMIC_DRAW);
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glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
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/* Advance the cursor to the start of the next character */
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x += (g->advance.x >> 6) * sx;
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y += (g->advance.y >> 6) * sy;
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}
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glDisableVertexAttribArray(attribute_coord);
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glDeleteTextures(1, &tex);
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}
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void display() {
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float sx = 2.0 / glutGet(GLUT_WINDOW_WIDTH);
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float sy = 2.0 / glutGet(GLUT_WINDOW_HEIGHT);
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glUseProgram(program);
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/* White background */
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glClearColor(1, 1, 1, 1);
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glClear(GL_COLOR_BUFFER_BIT);
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/* Enable blending, necessary for our alpha texture */
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glEnable(GL_BLEND);
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glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
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GLfloat black[4] = { 0, 0, 0, 1 };
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GLfloat red[4] = { 1, 0, 0, 1 };
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GLfloat transparent_green[4] = { 0, 1, 0, 0.5 };
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/* Set font size to 48 pixels, color to black */
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FT_Set_Pixel_Sizes(face, 0, 48);
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glUniform4fv(uniform_color, 1, black);
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/* Effects of alignment */
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render_text("The Quick Brown Fox Jumps Over The Lazy Dog", -1 + 8 * sx, 1 - 50 * sy, sx, sy);
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render_text("The Misaligned Fox Jumps Over The Lazy Dog", -1 + 8.5 * sx, 1 - 100.5 * sy, sx, sy);
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/* Scaling the texture versus changing the font size */
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render_text("The Small Texture Scaled Fox Jumps Over The Lazy Dog", -1 + 8 * sx, 1 - 175 * sy, sx * 0.5, sy * 0.5);
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FT_Set_Pixel_Sizes(face, 0, 24);
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render_text("The Small Font Sized Fox Jumps Over The Lazy Dog", -1 + 8 * sx, 1 - 200 * sy, sx, sy);
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FT_Set_Pixel_Sizes(face, 0, 48);
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render_text("The Tiny Texture Scaled Fox Jumps Over The Lazy Dog", -1 + 8 * sx, 1 - 235 * sy, sx * 0.25, sy * 0.25);
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FT_Set_Pixel_Sizes(face, 0, 12);
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render_text("The Tiny Font Sized Fox Jumps Over The Lazy Dog", -1 + 8 * sx, 1 - 250 * sy, sx, sy);
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FT_Set_Pixel_Sizes(face, 0, 48);
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/* Colors and transparency */
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render_text("The Solid Black Fox Jumps Over The Lazy Dog", -1 + 8 * sx, 1 - 430 * sy, sx, sy);
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glUniform4fv(uniform_color, 1, red);
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render_text("The Solid Red Fox Jumps Over The Lazy Dog", -1 + 8 * sx, 1 - 330 * sy, sx, sy);
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render_text("The Solid Red Fox Jumps Over The Lazy Dog", -1 + 28 * sx, 1 - 450 * sy, sx, sy);
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glUniform4fv(uniform_color, 1, transparent_green);
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render_text("The Transparent Green Fox Jumps Over The Lazy Dog", -1 + 8 * sx, 1 - 380 * sy, sx, sy);
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render_text("The Transparent Green Fox Jumps Over The Lazy Dog", -1 + 18 * sx, 1 - 440 * sy, sx, sy);
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glutSwapBuffers();
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}
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void free_resources() {
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glDeleteProgram(program);
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}
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int main(int argc, char *argv[]) {
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glutInit(&argc, argv);
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glutInitContextVersion(2,0);
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glutInitDisplayMode(GLUT_RGB);
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glutInitWindowSize(640, 480);
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glutCreateWindow("Basic Text");
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if (argc > 1)
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fontfilename = argv[1];
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else
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fontfilename = "FreeSans.ttf";
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GLenum glew_status = glewInit();
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if (GLEW_OK != glew_status) {
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fprintf(stderr, "Error: %s\n", glewGetErrorString(glew_status));
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return 1;
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}
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if (!GLEW_VERSION_2_0) {
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fprintf(stderr, "No support for OpenGL 2.0 found\n");
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return 1;
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}
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if (init_resources()) {
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glutDisplayFunc(display);
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glutMainLoop();
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}
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free_resources();
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return 0;
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}
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