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OpenGL Quick tutorial: Variable width bitmap fonts

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Guest Anonymous Poster   
Guest Anonymous Poster
Why not submit it for a sweet snippet?

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Promit    13246
Original post by Anonymous Poster
Why not submit it for a sweet snippet?

The turnover time between submission and posting is quite long. Besides, in a week or two it'll be available in a different, as-of-yet unannounced venue.

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evaclear    166
Maybe I'm missing something but is there any reason that your not doing any kerning? With out kerning being done certian letter pairs will always look a little odd for example "LI" can look like "L I" with out the propper kernining values or they can also appear to be too close to eachother. Kerning values are something you should be able to extract from the true type font on the export.

It's something you may want to consider doing along with a little bit of leding to adjust the space between multiple lines of text so that it's readable.

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gunning    749
Kerning information and line height is exported from BMFont and stored in the .fnt file. Promit already handles kerning and line height would only be an issue with multiple lines, which is fairly simple to implement, but not necessary for most non-rpg games.

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kiwibonga    183
Hey uh... I apologize for bringing this 7 year old post back from the grave, but it's still a top result on google (and/or linked on angelcode's download page)...

if anyone tried using Promit's code with the latest version of BMFont, you'll notice crashes, here's what to look out for:

1. There's an unhandled new key in the if( Read == "char") section called "chnl" -- just add another case for it

2. All the values in the file can be signed, so don't use the unsigned shorts from the CharDescriptor struct as-is (otherwise half your letters won't show up and you'll want to kill yourself). Like Promit, cast everything to float! (3 days of "where the flying **** is the letter P?")

3. First char is now systematically id -1 (or 65535 unsigned); that's not a valid array index -- it's data for the unicode "unknown character" character. Either skip it or save it separately, maybe a "defaultChar" variable somewhere...

That's my quick and dirty debugging advice... Take it or leave it. Sorry again for the gravedigging.

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Promit    13246

cool.png Don't worry, I just checked and this code is still driving the text rendering for our current gen engine. I think a few minor tweaks were made over the years, and that's it.

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vexe    241

Hey Promit, thanks for the tutorial. Helped me out remove dependecy to the font rendering libs I was using.


I was just wondering what does it take to include the font size with the vertices calculations to set the size of the printed font? do I just multiply by the font set size for each line of vertices calculation? or do I just multiply with a scale matrix?


Also, there's other values in the font format such as "aa", "stretchH", "lineHeight", "padding", "spacing", "scaleH" and "scaleW". I'm not sure where exactly each one of those fit into the picture?


Here's my rendering code, maybe someone will find it useful - or could suggest a better way/improvements. Currently I'm dynamically allocating the vertices/uv buffers, maybe I should just set a max value instead, but anyways...

void FontRender(font_renderer *Renderer, font_set *Font)
    u32 NumChars = StringLength(Renderer->Text);
    u32 BufferSize = NumChars * 12 * sizeof(r32);
    if (!Renderer->Initialized)
        glGenBuffers(1, &Renderer->VBO);
        glBindBuffer(GL_ARRAY_BUFFER, Renderer->VBO);
        glBufferData(GL_ARRAY_BUFFER, BufferSize * 2, 0, GL_DYNAMIC_DRAW);

        glGenVertexArrays(1, &Renderer->VAO);
        glVertexAttribPointer(0, 2, GL_FLOAT, 0, 0, 0);
        glVertexAttribPointer(1, 2, GL_FLOAT, 0, 0, (void *)BufferSize);

        glBindBuffer(GL_ARRAY_BUFFER, 0);

        Renderer->Initialized = 1;

    r32 *VertPos = Calloc(NumChars * 12, r32);
    r32 *VertUV = Calloc(NumChars * 12, r32);

    For(u32, i, NumChars)
        font_character Character = Font->Characters[Renderer->Text[i] - 32];
        r32 X = Character.X;
        r32 Y = Character.Y;
        r32 XOffset = Character.XOffset;
        r32 YOffset = Character.YOffset;
        r32 XAdvance = Character.XAdvance;
        r32 Width = Character.Width;
        r32 Height = Character.Height;

        // Triangle 1
            // Top Left
            VertPos[i * 12] = Renderer->CurrentX + XOffset;
            VertPos[i * 12 + 1] = YOffset;

            // Bottom Left
            VertPos[i * 12 + 2] = Renderer->CurrentX + XOffset;
            VertPos[i * 12 + 3] = YOffset + Height;

            // Bottom Right
            VertPos[i * 12 + 4] = Renderer->CurrentX + XOffset + Width;
            VertPos[i * 12 + 5] = YOffset + Height;

        // Triangle 2
            // Bottom Right
            VertPos[i * 12 + 6] = VertPos[i * 12 + 4];
            VertPos[i * 12 + 7] = VertPos[i * 12 + 5];

            // Top Right
            VertPos[i * 12 + 8] = Renderer->CurrentX + XOffset + Width;
            VertPos[i * 12 + 9] = YOffset;

            // Top Left
            VertPos[i * 12 + 10] = VertPos[i * 12];
            VertPos[i * 12 + 11] = VertPos[i * 12 + 1];

        // UV 1
            // Top left
            VertUV[i * 12] = X / Font->Width;
            VertUV[i * 12 + 1] = Y / Font->Height;

            // Bottom left
            VertUV[i * 12 + 2] = X / Font->Width;
            VertUV[i * 12 + 3] = (Y + Height) / Font->Height;

            // Bottom right
            VertUV[i * 12 + 4] = (X + Width) / Font->Width;
            VertUV[i * 12 + 5] = (Y + Height) / Font->Height;

        // UV 2
            // Bottom right
            VertUV[i * 12 + 6] = VertUV[i * 12 + 4];
            VertUV[i * 12 + 7] = VertUV[i * 12 + 5];

            // Top right
            VertUV[i * 12 + 8] = (X + Width) / Font->Width;
            VertUV[i * 12 + 9] = Y / Font->Height;

            // Top left
            VertUV[i * 12 + 10] = VertUV[i * 12 ];
            VertUV[i * 12 + 11] = VertUV[i * 12 + 1];

        Renderer->CurrentX += Character.XAdvance;

    glBindBuffer(GL_ARRAY_BUFFER, Renderer->VBO);
    u32 Offset = 0;
    glBufferSubData(GL_ARRAY_BUFFER, Offset, BufferSize, VertPos);
    Offset += BufferSize;
    glBufferSubData(GL_ARRAY_BUFFER, Offset, BufferSize, VertUV);

    m4 FontProjection = Orthographic(0, 800, 600, 0, -1, +1);

    ShaderSetV3(Renderer->Shader, "Color", Renderer->Color);
    ShaderSetM4(Renderer->Shader, "Projection", &FontProjection);
    glDrawArrays(GL_TRIANGLES, 0, NumChars * 6);

    glBindBuffer(GL_ARRAY_BUFFER, 0);
Edited by vexe

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