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 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 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 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 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 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<: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.