I'm trying to render a freetype font using OpenGL, following the example posted at http://en.wikibooks.org/wiki/OpenGL_Programming/Modern_OpenGL_Tutorial_Text_Rendering_02.
I've been able to generate a texture atlas from the font, creating shaders and creating quads. What I seem to get stuck at is passing the texture to the shader and/or getting the correct UVs for my quads. Been struggling for a good while now and really need the help.
The following is the struct I use to create my texture atlas.
struct FontCharacter
{
float advanceX;
float advanceY;
float bitmapWidth;
float bitmapHeight;
float bitmapLeft;
float bitmapTop;
float uvOffsetX;
float uvOffsetY;
};
struct FontTextureAtlas
{
GLuint texture;
GLuint textureUniform;
int width;
int height;
FontCharacter characters[128];
FontTextureAtlas(FT_Face face, int h, GLuint tUniform)
{
FT_Set_Pixel_Sizes(face, 0, h);
FT_GlyphSlot glyphSlot = face->glyph;
int roww = 0;
int rowh = 0;
width = 0;
height = 0;
memset(characters, 0, sizeof(FontCharacter));
for (int i = 32; i < 128; i++)
{
if (FT_Load_Char(face, i, FT_LOAD_RENDER))
{
std::cout << "Loading character %c failed\n", i;
continue;
}
if (roww + glyphSlot->bitmap.width + 1 >= MAX_WIDTH)
{
width = std::fmax(width, roww);
height += rowh;
roww = 0;
rowh = 0;
}
roww += glyphSlot->bitmap.width + 1;
rowh = std::fmax(rowh, glyphSlot->bitmap.rows);
}
width = std::fmax(width, roww);
height += rowh;
glGenTextures(1, &texture);
if (glGetError() != GL_NO_ERROR)
{
std::cout << "glGenTextures failed\n";
}
glActiveTexture(GL_TEXTURE0 + texture);
if (glGetError() != GL_NO_ERROR)
{
std::cout << "glActiveTexture failed\n";
}
glBindTexture(GL_TEXTURE_2D, texture);
if (glGetError() != GL_NO_ERROR)
{
std::cout << "glBindTexture failed\n";
}
glUniform1i(tUniform, 0);
textureUniform = tUniform;
glTexImage2D(GL_TEXTURE_2D, 0, GL_RED, width, height, 0, GL_RED, GL_UNSIGNED_BYTE, 0);
if (glGetError() != GL_NO_ERROR)
{
std::cout << "glTexImage2D failed\n";
}
glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
if (glGetError() != GL_NO_ERROR)
{
std::cout << "glPixelStorei failed\n";
}
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
if (glGetError() != GL_NO_ERROR)
{
std::cout << "glTexParameteri failed\n";
}
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
if (glGetError() != GL_NO_ERROR)
{
std::cout << "glTexParameteri failed\n";
}
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
if (glGetError() != GL_NO_ERROR)
{
std::cout << "glTexParameteri failed\n";
}
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
if (glGetError() != GL_NO_ERROR)
{
std::cout << "glTexParameteri failed\n";
}
int ox = 0;
int oy = 0;
rowh = 0;
for (int i = 32; i < 128; i++)
{
if (FT_Load_Char(face, i, FT_LOAD_RENDER))
{
std::cout << "Loading character %c failed\n", i;
continue;
}
if (ox + glyphSlot->bitmap.width + 1 >= MAX_WIDTH)
{
oy += rowh;
rowh = 0;
ox = 0;
}
glTexSubImage2D(GL_TEXTURE_2D, 0, ox, oy, glyphSlot->bitmap.width, glyphSlot->bitmap.rows, GL_RED, GL_UNSIGNED_BYTE, glyphSlot->bitmap.buffer);
if (glGetError() != GL_NO_ERROR)
{
std::cout << "BORKED AGAIN\n";
}
characters[i].advanceX = glyphSlot->advance.x >> 6;
characters[i].advanceY = glyphSlot->advance.y >> 6;
characters[i].bitmapWidth = glyphSlot->bitmap.width;
characters[i].bitmapHeight = glyphSlot->bitmap.rows;
characters[i].bitmapLeft = glyphSlot->bitmap_left;
characters[i].bitmapTop = glyphSlot->bitmap_top;
characters[i].uvOffsetX = ox / (float)width;
characters[i].uvOffsetY = oy / (float)height;
rowh = std::fmax(rowh, glyphSlot->bitmap.rows);
ox += glyphSlot->bitmap.width + 1;
}
std::cout << "Generated a " << width << "x " << height << " (" << width * height / 1024 << " kb) texture atlas.\n";
}
~FontTextureAtlas()
{
glDeleteTextures(1, &texture);
}
Local variables and function heads used in the renderer
class RenderCore
{
FT_Library library;
FT_Face face;
FontTextureAtlas* a48;
FontTextureAtlas* a24;
FontTextureAtlas* a12;
GLuint vbo;
GLuint vao;
GLuint m_posUV;
GLuint m_colorIN;
GLuint m_texture;
int InitFT();
void RenderText(const char* text, FontTextureAtlas* atlas, float x, float y, float sx, float sy);
}
This is where I load my fonts.
int RenderCore::InitFT()
{
if (FT_Init_FreeType(&library))
{
std::cout << "Could not Initialize freetype library.\n";
return 0;
}
/* Load a font */
if (FT_New_Face(library, "assets/Fonts/arialbd.ttf", 0, &face))
{
std::cout << "Could not open font assets/Fonts/DentonBeta2.ttf\n";
return 0;
}
m_shaderManager->CreateProgram("Text");
m_shaderManager->LoadShader("shaders/Text.vertex", "TextVS", GL_VERTEX_SHADER);
m_shaderManager->LoadShader("shaders/Text.fragment", "TextFS", GL_FRAGMENT_SHADER);
m_shaderManager->AttachShader("TextVS", "Text");
m_shaderManager->AttachShader("TextFS", "Text");
m_shaderManager->LinkProgram("Text");
m_shaderManager->UseProgram("Text");
m_shaderManager->UseProgram("Text");
m_colorIN = m_shaderManager->GetUniformLocation("Text", "inputColor");
m_texture = m_shaderManager->GetUniformLocation("Text", "texture");
// Create the vertex buffer object
glGenBuffers(1, &vbo);
glGenVertexArrays(1, &vao);
/* Create texture atlasses for several font sizes */
a48 = new FontTextureAtlas(face, 48, m_texture);
a24 = new FontTextureAtlas(face, 24, m_texture);
a12 = new FontTextureAtlas(face, 12, m_texture);
}
Rendering function.
void RenderCore::RenderText(const char* text, FontTextureAtlas* atlas, float x, float y, float sx, float sy)
{
m_shaderManager->UseProgram("Text");
const unsigned char* p;
std::vector<glm::vec4> coords;
int c = 0;
for (p = (const unsigned char*)text; *p; p++)
{
float x2 = x + atlas->characters[*p].bitmapLeft * sx;
float y2 = -y - atlas->characters[*p].bitmapTop * sy;
float w = atlas->characters[*p].bitmapWidth * sx;
float h = atlas->characters[*p].bitmapHeight * sy;
x += atlas->characters[*p].advanceX * sx;
y += atlas->characters[*p].advanceY * sy;
if (!w || !h)
continue;
coords.push_back(
glm::vec4(
x2,
-y2,
atlas->characters[*p].uvOffsetX,
atlas->characters[*p].uvOffsetY)
);
coords.push_back(
glm::vec4(
x2 + w,
-y2,
atlas->characters[*p].uvOffsetX + atlas->characters[*p].bitmapWidth / atlas->width,
atlas->characters[*p].uvOffsetY)
);
coords.push_back(
glm::vec4(
x2,
-y2 - h,
atlas->characters[*p].uvOffsetX,
atlas->characters[*p].uvOffsetY + atlas->characters[*p].bitmapHeight / atlas->height)
);
coords.push_back(
glm::vec4(
x2 + w,
-y2,
atlas->characters[*p].uvOffsetX + atlas->characters[*p].bitmapWidth / atlas->width,
atlas->characters[*p].uvOffsetY)
);
coords.push_back(
glm::vec4(
x2,
-y2 - h,
atlas->characters[*p].uvOffsetX,
atlas->characters[*p].uvOffsetY + atlas->characters[*p].bitmapHeight / atlas->height)
);
coords.push_back(
glm::vec4(
x2 + w,
-y2 - h,
atlas->characters[*p].uvOffsetX + atlas->characters[*p].bitmapWidth / atlas->width,
atlas->characters[*p].uvOffsetY + atlas->characters[*p].bitmapHeight / atlas->height)
);
}
glEnable(GL_BLEND);
glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
glActiveTexture(GL_TEXTURE0 + atlas->texture);
glUniform1i(atlas->textureUniform, 0);
glBindTexture(GL_TEXTURE_2D, atlas->texture);
m_shaderManager->SetUniform(1, glm::vec4(0, 0, 1, 1), m_colorIN);
glBindBuffer(GL_ARRAY_BUFFER, vbo);
glBufferData(GL_ARRAY_BUFFER, coords.size() * sizeof(glm::vec4), coords.data(), GL_DYNAMIC_DRAW);
//Generate VAO
glBindVertexArray(vao);
//Position
glEnableVertexAttribArray(0);
glVertexAttribPointer(0, 4, GL_FLOAT, GL_FALSE, sizeof(glm::vec4), (void*)0);
glBindVertexArray(vao);
glDrawArrays(GL_TRIANGLE_STRIP, 0, coords.size());
glDisableVertexAttribArray(0);
m_shaderManager->ResetProgram();
}
Vertex shader
#version 440
in vec4 pos_uv;
out vec2 uv;
void main()
{
gl_Position = vec4(pos_uv.xy, 0, 1);
uv = pos_uv.zw;
}
Fragment shader
#version 440
in vec2 uv;
uniform sampler2D texture;
uniform vec4 inputColor;
out vec4 color;
void main()
{
color = vec4(inputColor.rgb, texture2D(texture, uv).a);
}
Using gDebugger I can see the texture atlas having been generated properly and the VBO seems fine as well. The result is just a bunch of squares on screen however and I really have no idea why. I think it might be a problem with passing the texture to the shader, all channels except the alpha channel is empty and the alpha is always 1.
Managed to solve the problem, instead of glActiveTexture(GL_TEXTURE0 + texture); it should have only been glActiveTexture(GL_TEXTURE0);
I'm assuming glActiveTexture binds to a specific index within a program and not for all textures.
来源：https://stackoverflow.com/questions/20271331/opengl-font-rendering-using-freetype2