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OpenGL [Solved] Rendering text hits fps - hard.

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So I'm using opengl, wgl and c++ to render text. The code makes a call to glCallLists to render the text - so it shouldn't be too slow, right? Wrong. Has a rotating skybox (6 quads, 6 textures, texture size 1024x1024, linear filter), and 1/2/3 characters of text drawn in colour at the top right (represents fps). At this point, fps is between 70 and 90. Uh oh. Draw some untextured quads and lines (I tried just the console without text, it has no fps hit) and a whole bunch more text, fps down to a persistent 2. Not good. Here is the relevant code: The calls are made from Lua into c++, but I don't think the problem lies there as I'm also making tonnes of other calls (like drawing each line, each quad) that are still being made back when fps is up at 80. Just to put this in perspective, when I render 3x3 segments of terrain at the same time (each segment is 64x64 quads, textured, with lighting), fps is about 20. Surely rendering some simple text can't be more intensive than rendering a full 3D terrain with lighting? Here is the text code:
// Include header
#include "text.h"

// Define functions
int font_create( char* family, int size, int weight ) {
	HFONT font;
	HFONT oldfont;

	HDC hDC = GetHDC();

	int base = glGenLists( 96 );
	font = CreateFont( -size, 0, 0, 0, weight, false, false, false, 
	oldfont = (HFONT)SelectObject( hDC, font );
	wglUseFontBitmaps( hDC, 32, 96, base );
	SelectObject( hDC, oldfont );
	DeleteObject( font );

	return base;

void font_destroy( int id ) {
	glDeleteLists( id, 96 );

void font_render_noraster( char* text, int id ) {
	glPushAttrib( GL_LIST_BIT );
	glListBase( id-32 );
	glCallLists( strlen( text ), GL_UNSIGNED_BYTE, text );

void font_render( char* text, int id, int x, int y ) {
	glRasterPos2f( float( x ), float( y ) );
	font_render_noraster( text, id );

int font_getwidth( char* text, int id ) {

	GLint oldbuffer;
	glGetIntegerv( GL_DRAW_BUFFER, &oldbuffer );
	glDrawBuffer( GL_NONE );

	GLfloat o_rpos[4];
	glGetFloatv( GL_CURRENT_RASTER_POSITION, o_rpos );

	font_render_noraster( text, id );

	GLfloat n_rpos[4];
	glGetFloatv( GL_CURRENT_RASTER_POSITION, n_rpos );

	glDrawBuffer( oldbuffer );

	return int( n_rpos[0] - o_rpos[0] );

Here is the lua binding:
static int lbind_r_rendertext( lua_State* L ) {
	char* text = const_cast<char*>( luaL_checkstring( L, 1 ) );
	int base = luaL_checkint( L, 2 );
	int x = luaL_checkint( L, 3 );
	int y = luaL_checkint( L, 4 );
	font_render( text, base, x, y );
	return 0;

Perhaps it doesn't like the const_cast much? Any ideas? [Edited by - thomasfn1 on April 1, 2010 2:03:54 PM]

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Can you try a profiler or something to see if there is something obvious causing that perf hit? I use a similar method to render text and I've never seen any kind of performance hit from it.

I think something else has to be going on, because that shouldn't be that slow, unless you're calling font_create every frame or something.

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I'll do some more debugging to see if something silly like font_create being called every frame is happening. I'm not sure on the best way of implementing a profiler, I guess I could make something that records time differences between operations and writes it to the log but it isn't practical (especially since what gets written to the log gets written to that console too :P)

I also tried not casting into char* at the lua binding and keeping it as const char* and passing that into glCallLists instead, had no effect.

font_create is getting called once, at the beginning of the program, as expected.

And who uses html in forum code anyways -_-

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Thanks - suitable name methinks. I'll have a go now - but I'll have to go soon, so I might not get back to you until tommorow.


I ran it over a 10 second period, with the console rendering all the text.

Profiler Result

I'm not sure what it all means :/

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Anyone got any more ideas? I replaced the text size calculation code with GetTextExtentPoint, it apparently works, nothing's moved off to weird places. But I'm still having problems with the fps levels.

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As soon as I saw "glRasterPos2f" alarm bells started ringing and so I have an idea; don't use wglUseFontBitmaps to generate your text.

A quick look at the MSDN page on it hightlights the problem;

Each display list consists of a single call to glBitmap

That is going to be a killer. The function is old and is going to hurt as its probably poorly optimised/implimented in modern systems, not to mention it probably sends a bitmap over the bus to the card for every call, even in a display list its not going to be fast.

The fastest way to render text is to create a texture with each character on (or more than one texture in the case of larger fonts), then build the list of tris or quads which access this texture at the right point to grab the letters and render them to the screen; it will be faster.

  • Instead of wglUseFontBitmaps maybe try wglUseFontOutlines? I use that currently and I've never noticed any slowdown from it. I've tried building my own text from a character map texture, but I always thought that looked like crap unless I used a huge texture to store the text (either too jagged or too blurred with AA)

    Heres a setup test you can quickly drop in to test to see if its any faster for you.

    void GfxOpenGL::BuildOutlineFont(){

    HFONT font;
    base_ = glGenLists(256);
    font = CreateFont( -24, // Height Of Font
    0, // Width Of Font
    0, // Angle Of Escapement
    0, // Orientation Angle
    400, // Font Weight
    FALSE, // Italic
    FALSE, // Underline
    FALSE, // Strikeout
    ANSI_CHARSET, // Character Set Identifier
    OUT_TT_PRECIS, // Output Precision
    CLIP_DEFAULT_PRECIS, // Clipping Precision
    0, // Output Quality
    FF_DONTCARE|DEFAULT_PITCH, // Family And Pitch
    "Arial"); // Font Name

    wglUseFontOutlines( hDC, // Select The Current DC
    0, // Starting Character
    255, // Number Of Display Lists To Build
    base_, // Starting Display Lists
    0.8f, // Deviation From The True Outlines
    0.2f, // Font Thickness In The Z Direction
    WGL_FONT_POLYGONS, // Use Polygons, Not Lines
    gmf); // Address Of Buffer To Recieve Data


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    I use the wglUseFontBitmaps method on a pretty recent card.

    About 1000 glyphs displayed: 100 fps to 80 fps drop.

    Nowhere near the 70-2 stuff. That old and nasty ugly bitmap/displaylist stuff should work much faster.

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    I'm working on a pretty old laptop: 768mb ram, 2.8ghz single core, ati radeon mobility 7000. But still, the drop is ridiculous. I've been messing with using texture mapped fonts, once I get the damn thing to compile, I'll see how that works out. I'll try the outlined fonts in a sec.

    Probably something todo with that glyph metrics float structure thing.

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    Ok so nevermind that error - I just allocated the structure to the heap and stopped that error. But then, as soon as the code returns out of that function, it gives me debug assertion failure (with no information). I'm also giving up on the bitmapped fonts, as that's giving me random debug assertion failures all over the place - when returning stuff from functions mostly.

    I'm really at a loss here :(

    I am an idiot. You pass an array to that function.

    Ok now it compiles and runs with the Outlines. But rendering text now glitches up everything; the only thing that renders is my console window and a few random lines, and there are some inexplicable dots at the top of the screen. I suspect the lists generated contains some translation call that's messing stuff up; I'll investigate. Thanks for your help guys.

    Wrapping the list call in PushMatrix and PopMatrix doesn't work.

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    Just a quick observation..

    glListBase( id-32 );
    glCallLists( strlen( text ), GL_UNSIGNED_BYTE, text );

    You can sub 32 from id after creation and add 32 before deletion.
    That way to save a couple of clocks, but the real killer is strlen.
    (Besides all the hidden code of course)

    I wrote a couple of font rendering method tests in assembler...
    (You need to register/logon to download source files)

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    Original post by Vortez
    You should use this tutorial from nehe instead, the fonts looks ways better, and the best is they can scale if ur willing to tweak the code a bit. Im using it in my engine and don't see any performance hit like i did with the wglUseFontBitmaps method.

    Yea I had a look at that tutorial and got as far as downloading freetype and linking it before I got distracted with something else. I'll have a crack at implementing it if UseFontOutlines fails me.

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    Good news! I got it to work! Thanks guys for all your help.

    In case someone wants to know, I had all the font handling code in a class and I wasn't allocating the class objects to the heap so bits of the class memory were getting used for other things. Including the list base.

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        m_pPSO->CreateShaderResourceBinding(&m_pSRB); Note that an SRB is only compatible with the pipeline state it was created from. SRB object inherits all static bindings from shaders in the pipeline, but is not allowed to change them.
        Mutable resources can only be set once for every instance of a shader resource binding. Such resources are intended to define specific material properties. For instance, a diffuse texture for a specific material is not expected to change once the material is defined and can be set right after the SRB object has been created:
        m_pSRB->GetVariable(SHADER_TYPE_PIXEL, "tex2DDiffuse")->Set(pDiffuseTexSRV); In some cases it is necessary to bind a new resource to a variable every time a draw command is invoked. Such variables should be labeled as dynamic, which will allow setting them multiple times through the same SRB object:
        m_pSRB->GetVariable(SHADER_TYPE_VERTEX, "cbRandomAttribs")->Set(pRandomAttrsCB); Under the hood, the engine pre-allocates descriptor tables for static and mutable resources when an SRB objcet is created. Space for dynamic resources is dynamically allocated at run time. Static and mutable resources are thus more efficient and should be used whenever possible.
        As you can see, Diligent Engine does not expose low-level details of how resources are bound to shader variables. One reason for this is that these details are very different for various APIs. The other reason is that using low-level binding methods is extremely error-prone: it is very easy to forget to bind some resource, or bind incorrect resource such as bind a buffer to the variable that is in fact a texture, especially during shader development when everything changes fast. Diligent Engine instead relies on shader reflection system to automatically query the list of all shader variables. Grouping variables based on three types mentioned above allows the engine to create optimized layout and take heavy lifting of matching resources to API-specific resource location, register or descriptor in the table.
        This post gives more details about the resource binding model in Diligent Engine.
        Setting the Pipeline State and Committing Shader Resources
        Before any draw or compute command can be invoked, the pipeline state needs to be bound to the context:
        m_pContext->SetPipelineState(m_pPSO); Under the hood, the engine sets the internal PSO object in the command list or calls all the required native API functions to properly configure all pipeline stages.
        The next step is to bind all required shader resources to the GPU pipeline, which is accomplished by IDeviceContext::CommitShaderResources() method:
        m_pContext->CommitShaderResources(m_pSRB, COMMIT_SHADER_RESOURCES_FLAG_TRANSITION_RESOURCES); The method takes a pointer to the shader resource binding object and makes all resources the object holds available for the shaders. In the case of D3D12, this only requires setting appropriate descriptor tables in the command list. For older APIs, this typically requires setting all resources individually.
        Next-generation APIs require the application to track the state of every resource and explicitly inform the system about all state transitions. For instance, if a texture was used as render target before, while the next draw command is going to use it as shader resource, a transition barrier needs to be executed. Diligent Engine does the heavy lifting of state tracking.  When CommitShaderResources() method is called with COMMIT_SHADER_RESOURCES_FLAG_TRANSITION_RESOURCES flag, the engine commits and transitions resources to correct states at the same time. Note that transitioning resources does introduce some overhead. The engine tracks state of every resource and it will not issue the barrier if the state is already correct. But checking resource state is an overhead that can sometimes be avoided. The engine provides IDeviceContext::TransitionShaderResources() method that only transitions resources:
        m_pContext->TransitionShaderResources(m_pPSO, m_pSRB); In some scenarios it is more efficient to transition resources once and then only commit them.
        Invoking Draw Command
        The final step is to set states that are not part of the PSO, such as render targets, vertex and index buffers. Diligent Engine uses Direct3D11-syle API that is translated to other native API calls under the hood:
        ITextureView *pRTVs[] = {m_pRTV}; m_pContext->SetRenderTargets(_countof( pRTVs ), pRTVs, m_pDSV); // Clear render target and depth buffer const float zero[4] = {0, 0, 0, 0}; m_pContext->ClearRenderTarget(nullptr, zero); m_pContext->ClearDepthStencil(nullptr, CLEAR_DEPTH_FLAG, 1.f); // Set vertex and index buffers IBuffer *buffer[] = {m_pVertexBuffer}; Uint32 offsets[] = {0}; Uint32 strides[] = {sizeof(MyVertex)}; m_pContext->SetVertexBuffers(0, 1, buffer, strides, offsets, SET_VERTEX_BUFFERS_FLAG_RESET); m_pContext->SetIndexBuffer(m_pIndexBuffer, 0); Different native APIs use various set of function to execute draw commands depending on command details (if the command is indexed, instanced or both, what offsets in the source buffers are used etc.). For instance, there are 5 draw commands in Direct3D11 and more than 9 commands in OpenGL with something like glDrawElementsInstancedBaseVertexBaseInstance not uncommon. Diligent Engine hides all details with single IDeviceContext::Draw() method that takes takes DrawAttribs structure as an argument. The structure members define all attributes required to perform the command (primitive topology, number of vertices or indices, if draw call is indexed or not, if draw call is instanced or not, if draw call is indirect or not, etc.). For example:
        DrawAttribs attrs; attrs.IsIndexed = true; attrs.IndexType = VT_UINT16; attrs.NumIndices = 36; attrs.Topology = PRIMITIVE_TOPOLOGY_TRIANGLE_LIST; pContext->Draw(attrs); For compute commands, there is IDeviceContext::DispatchCompute() method that takes DispatchComputeAttribs structure that defines compute grid dimension.
        Source Code
        Full engine source code is available on GitHub and is free to use. The repository contains two samples, asteroids performance benchmark and example Unity project that uses Diligent Engine in native plugin.
        AntTweakBar sample is Diligent Engine’s “Hello World” example.

        Atmospheric scattering sample is a more advanced example. It demonstrates how Diligent Engine can be used to implement various rendering tasks: loading textures from files, using complex shaders, rendering to multiple render targets, using compute shaders and unordered access views, etc.

        Asteroids performance benchmark is based on this demo developed by Intel. It renders 50,000 unique textured asteroids and allows comparing performance of Direct3D11 and Direct3D12 implementations. Every asteroid is a combination of one of 1000 unique meshes and one of 10 unique textures.

        Finally, there is an example project that shows how Diligent Engine can be integrated with Unity.

        Future Work
        The engine is under active development. It currently supports Windows desktop, Universal Windows and Android platforms. Direct3D11, Direct3D12, OpenGL/GLES backends are now feature complete. Vulkan backend is coming next, and support for more platforms is planned.
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