love-demo2/src/font.cpp

#include <assert.h>
#include <stdlib.h>
#include <stdio.h>

#include "directxmath/directxmath.h"
#include "glad/gl.h"
#include "opengl.h"
#include "file.h"

#include "font.h"
#include "window.h"

namespace font {

  struct location {
    struct {
      unsigned int transform;
      unsigned int texture_sampler;
      unsigned int cell;
      unsigned int glyph;
    } uniform;
  };

  static location location;

  static unsigned int font_program = -1;

  void load_shader()
  {
    unsigned int program = compile_from_files("shader/font.vert",
                                              NULL, // geom
                                              "shader/font.frag");

    location.uniform.transform = glGetUniformLocation(program, "Transform");
    location.uniform.texture_sampler = glGetUniformLocation(program, "TextureSampler");
    location.uniform.cell = glGetUniformLocation(program, "Cell");
    location.uniform.glyph = glGetUniformLocation(program, "Glyph");
    printf("font program:\n");
    printf(" uniforms:\n  transform %u\n  texture_sampler %u\n  cell %u\n  glyph %u\n",
           location.uniform.transform,
           location.uniform.texture_sampler,
           location.uniform.cell,
           location.uniform.glyph
           );

    font_program = program;
  }

  font load_font(font_desc const& desc)
  {
    unsigned int texture;
    glGenTextures(1, &texture);
    glActiveTexture(GL_TEXTURE0);
    glBindTexture(GL_TEXTURE_2D, texture);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);

    int texture_data_size;
    void * texture_data = read_file(desc.path, &texture_data_size);
    assert(texture_data != nullptr);

    int width = desc.texture_width;
    int height = desc.texture_height;
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RED, width, height, 0, GL_RED, GL_UNSIGNED_BYTE, texture_data);

    free(texture_data);

    glBindTexture(GL_TEXTURE_2D, 0);

    return (font){
      .desc = &desc,
      .texture = texture,
      .stride = desc.texture_width / desc.glyph_width,
      .cell = { (float)desc.glyph_width / (float)desc.texture_width,
                (float)desc.glyph_height / (float)desc.texture_height },
    };
  }

  static inline int min(int a, int b)
  {
    return a < b ? a : b;
  }

  int best_font(font_desc const * const descs, int length)
  {
    int dimension = min(window::width, window::height);
    int ideal_height = (16 * dimension) / 1024;
    //printf("ideal_height: %d\n", ideal_height);
    int nearest = dimension;
    int nearest_ix = -1;
    for (int i = 0; i < length; i++) {
      font_desc const& desc = descs[i];
      int distance = abs(desc.glyph_height - ideal_height);
      if (distance < nearest) {
        nearest = distance;
        nearest_ix = i;
      }
    }
    assert(nearest_ix != -1);
    //printf("selected %d\n", descs[nearest_ix].glyph_height);
    return nearest_ix;
  }

  void load_fonts(font * const fonts, font_desc const * const descs, int length)
  {
    for (int i = 0; i < length; i++) {
      fonts[i] = load_font(descs[i]);
    }
  }

  inline static XMFLOAT2 glyph_coordinate(font const& font, int ord)
  {
    int c = ord - 32;
    int x = c % font.stride;
    int y = c / font.stride;
    XMVECTOR coord = XMVectorSet(x, y, 0, 0);
    XMFLOAT2 coordf;
    XMStoreFloat2(&coordf, coord);
    return coordf;
  }

  inline static XMFLOAT4X4 glyph_transform(font const& font, int x, int y)
  {
    XMMATRIX transform =
      XMMatrixScaling(font.desc->glyph_width, font.desc->glyph_height, 0)
      * XMMatrixTranslation(x, -y, 0)
      * XMMatrixScaling(2.0f / window::width, 2.0f / window::height, 0)
      * XMMatrixTranslation(-1, 1, 0);
    XMFLOAT4X4 transformf;
    XMStoreFloat4x4(&transformf, transform);
    return transformf;
  }

  void draw_start(font const& font, unsigned int vertex_array_object, unsigned int index_buffer)
  {
    glUseProgram(font_program);
    glDepthFunc(GL_ALWAYS);

    glActiveTexture(GL_TEXTURE0);
    glBindTexture(GL_TEXTURE_2D, font.texture);

    glUniform1i(location.uniform.texture_sampler, 0);
    glUniform2fv(location.uniform.cell, 1, (float *)&font.cell);

    glBindVertexArray(vertex_array_object);
    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, index_buffer);
  }

  void draw_string(font const& font, char const * const s, int x, int y)
  {
    int i = 0;
    while (s[i] != 0) {
      char c = s[i++];
      if (!(c <= 0x20 || c > 0x7f)) {
        XMFLOAT4X4 transform = glyph_transform(font, x, y);
        glUniformMatrix4fv(location.uniform.transform, 1, GL_FALSE, (float *)&transform);
        XMFLOAT2 glyph = glyph_coordinate(font, c);
        glUniform2fv(location.uniform.glyph, 1, (float *)&glyph);

        glDrawElements(GL_TRIANGLE_STRIP, 4, GL_UNSIGNED_BYTE, (void *)0);
      }

      x += font.desc->glyph_width;
    }
  }
}