# OpenGL Troubles with FTGL and OpenGL

This topic is 4244 days old which is more than the 365 day threshold we allow for new replies. Please post a new topic.

## Recommended Posts

I am trying to use FTGL with OpenGL, to do some simple font testing. (I'm using SDL as my context.) Unfortunatly, when I compile and run, I see no text. I'm doing everything right according to the FTGL FAQ and readme. I've also tried multiple differente methods of glOrtho'ing, different MaxtrixMode and stuff. Here's the source:
#include <stdio.h> #include <stdlib.h> #include <string.h> #include <math.h> #include "SDL.h" #include "OpenGL/gl.h" #include "OpenGL/glu.h" #include "IL/il.h" #include "IL/ilu.h" #include "IL/ilut.h" #include "FTGL_all.h" int timeToQuit = 0; FTGLBitmapFont font("/System/Library/Fonts/Geneva.dfont"); /* Set up SDL, OpenGL & DevIL video stuff. */ void setupVideo(int width_sv, int height_sv, int bpp_sv, int fullscreen_sv) { /* SDL. */ SDL_Init(SDL_INIT_VIDEO); if (fullscreen_sv > 0) { SDL_SetVideoMode(width_sv, height_sv, bpp_sv, SDL_OPENGL | SDL_HWSURFACE | SDL_FULLSCREEN); } else { SDL_SetVideoMode(width_sv, height_sv, bpp_sv, SDL_OPENGL | SDL_HWSURFACE); } /* OpenGL. */ glViewport(0, 0, width_sv, height_sv); glEnable(GL_TEXTURE_2D); glMatrixMode(GL_PROJECTION); glLoadIdentity(); gluOrtho2D(0.0, width_sv, height_sv, 0.0); glMatrixMode(GL_MODELVIEW); glClearColor(0.0f, 0.0f, 0.0f, 0.0f); glClearDepth(0.0f); /* DevIL. */ ilInit(); iluInit(); ilutInit(); ilutRenderer(ILUT_OPENGL); } /* Drawing function. */ void display() { glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); font.Render("Hello, World!"); glFlush(); SDL_GL_SwapBuffers(); } int main(int argc, char *argv[]) { setupVideo(320, 240, 32, 0); //glMatrixMode(GL_PROJECTION); //glLoadIdentity(); //gluOrtho2D(0.0, 1.0, 1.0, 0.0); //glTranslatef(0.5, 0.5, 0.5); font.FaceSize(14); while (timeToQuit != 1) { display(); } return(0); } [/QUOTE] The matrix block in main is where I try different modes and stuff. As I understand it, GL_MODELVIEW is for drawing models and stuff, and projection is where I'd manage my "camera", this is correct, no? And does glTranslatef move the position of where things will be drawn, or move the viewport through 3D space? Sorry, I understand this, but only vaguely. I promise, I did read the chapter in the red book about this, but at the end I still wasn't sure what was going on, in a sense. Thanks!

##### Share on other sites
GL_PROJECTION is to set the projection matrix so you would call that matrix and then call gluPerspective or Ortho or glFrustum() ect...

For your glTranslatef() that will move to the point you want and then make that point the current drawing location for your model, texture, whatever. It affects all matrices. So if you are drawing many objects you will need to look into

glPushMatrix()
and
glPopMatrix()

think of them as a way to reset the modelview without resetting it all to zero and losing your positions for all the objects you already have drawn. As for FTGL I can't comment I haven't used it, maybe someone else can help you who has...

##### Share on other sites
Ok, hang on. I'm still not quite sure I get it. o_0

When drawing a model, of say... a tree in a game It would be sorta like this, no?

glMatrixMode(GL_MODELVIEW);
glTranslatef(treeX, treeY, treeZ);
drawMyTree();

But if I then went to GL_PROJECTION (where I would put my "camera" stuff, as I understand it), the coords would still be loaded onto glTranslate, the ones I just setup, is that what you mean?

But if I say wanted to do multiple models, I could just do this, no?

glMatrixMode(GL_MODELVIEW);
glTranslatef(model1x, model1y, model1z);
drawModel1();
glTranslatef(model2x, model2y, model2z);
drawModel2();

And then so on and so forth, correct?

Anyway, related to FTGL, I inserted an SDL_delay command into my display loop, and now I see my font, rendered on the screen. Then it loops, and draws it again, but this time... to the right more. Is FTGL using my translate's, or just moving right, assuming that I'm just adding more words on, like in standard writing?

Thanks!

##### Share on other sites
When you call your camera code it is done in the modelview also. Now the code you posted about the models and translatef is correct but like I said you are going to end up wanting to use glPushMatrix() and glPopMatrix()...

glMatrixMode(GL_MODELVIEW);//reset viewport to our original viewport sizeglViewport(0, 0, gWidth, gHeight);glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);glLoadIdentity();	g_Camera.LookAt();glPushMatrix();glTranslatef(model1x, model1y, model1z);drawModel1();glPopMatrix();glPushMatrix();glTranslatef(model2x, model2y, model2z);drawModel2();glPopMatrix();

HTH

##### Share on other sites
I'm pretty sure FTGLBitmapFont needs to use some OpenGL functions in its constructor. As of right now it is being created before you have a valid OpenGL context. OpenGL calls are ignored if there is no valid context. - Nevermind, it's done in FaceSize.

Also, you will need to position it with glRasterPos* since it is a bitmap font.

EDIT:
Quote:
 Original post by OneMoreToGoAnyway, related to FTGL, I inserted an SDL_delay command into my display loop, and now I see my font, rendered on the screen. Then it loops, and draws it again, but this time... to the right more. Is FTGL using my translate's, or just moving right, assuming that I'm just adding more words on, like in standard writing?
Whoops, I missed that the first time. Ignore the part above about creating the font. Using glRasterPos* still stands however. The reason you see the font moving to the right is because when doing any bitmap drawing in OpenGL it moves the raster position to the end of what you drew, so each drawn character moves the raster position to the correct spot for the next character. This means the raster position will be at the end of the string you previously drew unless you set it to something else.

##### Share on other sites
Oh, ok. Thanks! I still have a lot to learn about the various positioning and matrix systems of OpenGL. :)

One question left:

So, translatef moves the paintbrush (in a sense), and the next drawn thing will be "painted" there. glRasterpos does the same but for another type of drawing.

No, I'm pretty sure the red book shows glTranslateF being used to move the "camera" around..., is that in the GL_PROJECTION matrix? Cause right now, that's where I do all my drawing... as that's what the examples on the web seem to always demonstrate. Is that sufficient, or shall we say... wise, for simple 2D scrollers and stuff? It seems to work.

Thanks!

##### Share on other sites
Oh, ok. Thanks! I still have a lot to learn about the various positioning and matrix systems of OpenGL. :)

One question left:

So, translatef moves the paintbrush (in a sense), and the next drawn thing will be "painted" there. glRasterpos does the same but for another type of drawing.

No, I'm pretty sure the red book shows glTranslateF being used to move the "camera" around..., is that in the GL_PROJECTION matrix? Cause right now, that's where I do all my drawing... as that's what the examples on the web seem to always demonstrate. Is that sufficient, or shall we say... wise, for simple 2D scrollers and stuff? It seems to work.

Thanks!

##### Share on other sites
Quote:
 Original post by OneMoreToGo...So, translatef moves the paintbrush (in a sense), and the next drawn thing will be "painted" there. glRasterpos does the same but for another type of drawing...
All glTranslate* does is multiply the current matrix by a translation matrix. This is almost always used on only the modelview matrix. Vertices are transformed by the modelview matrix when they are sent to OpenGL, this has the effect of translating an object by the amount specified (or translating the camera by the negative amount specified, see below).

glRasterPos* sets the raster position. The raster position is treated exactly like a vertex so you can think of it as glVertex* only for the bitmap and pixel drawing operations (ie: glDrawPixels) instead of geometry rendering. Since it is treated exactly like a vertex (it is transformed, clipped, lit, textured, etc the same way) there are some things to watch out for that may not be obvious. Read through "Avoiding 16 Common OpenGL Pitfalls" to learn about some of them, and other common mistakes.
Quote:
 Original post by OneMoreToGo...No, I'm pretty sure the red book shows glTranslateF being used to move the "camera" around..., is that in the GL_PROJECTION matrix? Cause right now, that's where I do all my drawing... as that's what the examples on the web seem to always demonstrate. Is that sufficient, or shall we say... wise, for simple 2D scrollers and stuff? It seems to work...
This is another common mistake. The projection matrix is meant just for projection matrices. That means you should only be using glFrustum/gluPerspective/glOrtho/gluOrtho2D on the projection matrix unless you know exactly what you're doing (custom projection matrices can be useful in some cases, but those cases are very rare). Read "Help stamp out GL_PROJECTION abuse" for more detailed information about why that is.

You also need to remember that OpenGL has no notion of a "camera," per se. There's just the modelview matrix. This should contain both the modeling transformation (transforms objects from model space to world space) and the viewing transformation (transforms objects from world space to view space). Now since there's no "camera" there is only one matrix. So anything you do on the modelview matrix can be thought of as affecting either the object or the camera in some way. Now imagine a camera pointing at some object. Moving the object some distance in one direction will produce the same result as moving the camera the same distance in the opposite direction. This is why a view matrix is really the inverse of what you would think it would be if you thought of the camera as any other object.

I know this is all very confusing at first. Hopefully that helped to clear it up a little bit instead of confuse more (I'm bad at explaining things sometimes). I recommend reading the first few major sections of Chapter 3 in the Red Book (that's for OpenGL 1.1, if you have a copy of a newer version I recommend using that instead) several times until it starts to sink in. If you have any more questions you can PM me or create a new thread here and either myself or someone else will try to help you out.

##### Share on other sites
Thank you, kalidor, for those links. I have actually read the text about stamping about GL_PROJECTION abuse, but then went on to read another that contradicted said text, so naturally, I was a bit confused. You mentioned that the projection matrix should only be used for glOrtho and related commands, is it ok to use those commands in my modelview matrix aswell? I kinda like drawing with pixel measurements rather that 0.2, 0.3 or 0.9 (for example).

Also, some fonts (like textuxe mapped) appear upside down, and it positions they should not. I know this is because I use the top left as (0,0), and not the bottom left as those fonts think I am using. I'm going to take a wild guess and assume that I can just switch up my glOrtho settings for drawing those, and then revert them.

• 12
• 10
• 11
• 18
• 13
• ### Similar Content

• Good Evening,
I want to make a 2D game which involves displaying some debug information. Especially for collision, enemy sights and so on ...
First of I was thinking about all those shapes which I need will need for debugging purposes: circles, rectangles, lines, polygons.
I am really stucked right now because of the fundamental question:
Where do I store my vertices positions for each line (object)? Currently I am not using a model matrix because I am using orthographic projection and set the final position within the VBO. That means that if I add a new line I would have to expand the "points" array and re-upload (recall glBufferData) it every time. The other method would be to use a model matrix and a fixed vbo for a line but it would be also messy to exactly create a line from (0,0) to (100,20) calculating the rotation and scale to make it fit.
If I proceed with option 1 "updating the array each frame" I was thinking of having 4 draw calls every frame for the lines vao, polygons vao and so on.
In addition to that I am planning to use some sort of ECS based architecture. So the other question would be:
Should I treat those debug objects as entities/components?
For me it would make sense to treat them as entities but that's creates a new issue with the previous array approach because it would have for example a transform and render component. A special render component for debug objects (no texture etc) ... For me the transform component is also just a matrix but how would I then define a line?
Treating them as components would'nt be a good idea in my eyes because then I would always need an entity. Well entity is just an id !? So maybe its a component?
Regards,
LifeArtist
• By QQemka
Hello. I am coding a small thingy in my spare time. All i want to achieve is to load a heightmap (as the lowest possible walking terrain), some static meshes (elements of the environment) and a dynamic character (meaning i can move, collide with heightmap/static meshes and hold a varying item in a hand ). Got a bunch of questions, or rather problems i can't find solution to myself. Nearly all are deal with graphics/gpu, not the coding part. My c++ is on high enough level.
Let's go:
Heightmap - i obviously want it to be textured, size is hardcoded to 256x256 squares. I can't have one huge texture stretched over entire terrain cause every pixel would be enormous. Thats why i decided to use 2 specified textures. First will be a tileset consisting of 16 square tiles (u v range from 0 to 0.25 for first tile and so on) and second a 256x256 buffer with 0-15 value representing index of the tile from tileset for every heigtmap square. Problem is, how do i blend the edges nicely and make some computationally cheap changes so its not obvious there are only 16 tiles? Is it possible to generate such terrain with some existing program?
Collisions - i want to use bounding sphere and aabb. But should i store them for a model or entity instance? Meaning i have 20 same trees spawned using the same tree model, but every entity got its own transformation (position, scale etc). Storing collision component per instance grats faster access + is precalculated and transformed (takes additional memory, but who cares?), so i stick with this, right? What should i do if object is dynamically rotated? The aabb is no longer aligned and calculating per vertex min/max everytime object rotates/scales is pretty expensive, right?
Drawing aabb - problem similar to above (storing aabb data per instance or model). This time in my opinion per model is enough since every instance also does not have own vertex buffer but uses the shared one (so 20 trees share reference to one tree model). So rendering aabb is about taking the model's aabb, transforming with instance matrix and voila. What about aabb vertex buffer (this is more of a cosmetic question, just curious, bumped onto it in time of writing this). Is it better to make it as 8 points and index buffer (12 lines), or only 2 vertices with min/max x/y/z and having the shaders dynamically generate 6 other vertices and draw the box? Or maybe there should be just ONE 1x1x1 cube box template moved/scaled per entity?
What if one model got a diffuse texture and a normal map, and other has only diffuse? Should i pass some bool flag to shader with that info, or just assume that my game supports only diffuse maps without fancy stuff?
There were several more but i forgot/solved them at time of writing
• By RenanRR
Hi All,
I'm reading the tutorials from learnOpengl site (nice site) and I'm having a question on the camera (https://learnopengl.com/Getting-started/Camera).
I always saw the camera being manipulated with the lookat, but in tutorial I saw the camera being changed through the MVP arrays, which do not seem to be camera, but rather the scene that changes:
#version 330 core layout (location = 0) in vec3 aPos; layout (location = 1) in vec2 aTexCoord; out vec2 TexCoord; uniform mat4 model; uniform mat4 view; uniform mat4 projection; void main() { gl_Position = projection * view * model * vec4(aPos, 1.0f); TexCoord = vec2(aTexCoord.x, aTexCoord.y); } then, the matrix manipulated:
..... glm::mat4 projection = glm::perspective(glm::radians(fov), (float)SCR_WIDTH / (float)SCR_HEIGHT, 0.1f, 100.0f); ourShader.setMat4("projection", projection); .... glm::mat4 view = glm::lookAt(cameraPos, cameraPos + cameraFront, cameraUp); ourShader.setMat4("view", view); .... model = glm::rotate(model, glm::radians(angle), glm::vec3(1.0f, 0.3f, 0.5f)); ourShader.setMat4("model", model);
So, some doubts:
- Why use it like that?
- Is it okay to manipulate the camera that way?
-in this way, are not the vertex's positions that changes instead of the camera?
- I need to pass MVP to all shaders of object in my scenes ?

What it seems, is that the camera stands still and the scenery that changes...
it's right?

Thank you

• Sampling a floating point texture where the alpha channel holds 4-bytes of packed data into the float. I don't know how to cast the raw memory to treat it as an integer so I can perform bit-shifting operations.

int rgbValue = int(textureSample.w);//4 bytes of data packed as color
// algorithm might not be correct and endianness might need switching.
vec3 extractedData = vec3(  rgbValue & 0xFF000000,  (rgbValue << 8) & 0xFF000000, (rgbValue << 16) & 0xFF000000);
extractedData /= 255.0f;

• While writing a simple renderer using OpenGL, I faced an issue with the glGetUniformLocation function. For some reason, the location is coming to be -1.
Anyone has any idea .. what should I do?