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ScherzkeCks

OpenGL
[Solved]Can't render Text

12 posts in this topic

Hi everybody,

 

I have been staring at this code for 3 days now and rewritten it 2 times with no effect. I know, that the texture and the shaders get loaded just fine (confirmed that using OpenGL Profiler on Mac). The shaders work as tested with my normal draws. But the function posted below doesn't put out anything. All the values in the vectors supplied to OpenGL are fine as well. I also tried using simple arrays instead of vectors(which shouldn't make a difference) to no avail. Can somebody tell me what it is?

bool Text::drawText(int x, int y, std::string text) {
	if (programID == 0)
	{
		return false;
	}
	if (textureID == 0)
	{
		return false;
	}

	int xOffset = 0;
    std::vector<glm::vec2> vertices;
    std::vector<glm::vec2> uvCoordinats;
	for (int i = 0; i < text.size(); ++i)
	{
		int id = text[i];
		for (int j = 0; j < glyphCount; ++j)
		{
			if (glyphs[j].id == id)
			{
				/**
				 * calculate vertices and stuff
				 * Layout is as follows:
				 *     v1    v2
				 *     ------
				 *     |  / |
				 *     | /  |
				 *     ------
				 *     v3    4
				 */
                
                
                glm::vec2 v1 = glm::vec2(x + xOffset + glyphs[j].xoffset, y + glyphs[j].yoffset);
                glm::vec2 v2 = glm::vec2(x + xOffset + glyphs[j].xoffset + glyphs[j].width, y + glyphs[j].yoffset);
                glm::vec2 v3 = glm::vec2(x + xOffset + glyphs[j].xoffset,y + glyphs[j].yoffset + glyphs[j].height);
                glm::vec2 v4 = glm::vec2(x + xOffset + glyphs[j].xoffset + glyphs[j].width, y + glyphs[j].yoffset + glyphs[j].height);
                
                vertices.push_back(v1);
                vertices.push_back(v2);
                vertices.push_back(v3);
                
                vertices.push_back(v3);
                vertices.push_back(v2);
                vertices.push_back(v4);
                
                glm::vec2 uv1 = glm::vec2((GLfloat)(glyphs[j].x)/ textureWidth, (GLfloat)(glyphs[j].y) / textureHeight);
                glm::vec2 uv2 = glm::vec2((GLfloat)(glyphs[j].x + glyphs[j].width) / textureWidth,(GLfloat)(glyphs[j].y) / textureHeight);
                glm::vec2 uv3 = glm::vec2((GLfloat)(glyphs[j].x) /textureWidth,(GLfloat)(glyphs[j].y + glyphs[j].height) /textureHeight);
                glm::vec2 uv4 = glm::vec2((GLfloat)(glyphs[j].x + glyphs[j].width) / textureWidth,(GLfloat)(glyphs[j].y + glyphs[j].height) /textureHeight);
                
                
                uvCoordinats.push_back(uv1);
                uvCoordinats.push_back(uv2);
                uvCoordinats.push_back(uv3);
                
                uvCoordinats.push_back(uv3);
                uvCoordinats.push_back(uv2);
                uvCoordinats.push_back(uv4);

                xOffset += glyphs[j].advance;
				break;
			}
		}
	}
    
    //time to draw
    glUseProgram(programID);
    
    glBindVertexArray(0);
    
    glActiveTexture(GL_TEXTURE0);
    glBindTexture(GL_TEXTURE_2D, textureID);
    GLuint textureSampler = glGetUniformLocation(programID,"myTextureSampler");
    glUniform1i(textureSampler,0);
    
    
    GLuint buffers[2];
    glGenBuffers(2,buffers);
    
    glEnableVertexAttribArray(RENDER_POSITION_LOCATION);
    glBindBuffer(GL_ARRAY_BUFFER,buffers[0]);
    glBufferData(GL_ARRAY_BUFFER,vertices.size() * sizeof(glm::vec2),&vertices[0],GL_STATIC_DRAW);
    glVertexAttribPointer(RENDER_POSITION_LOCATION,2,GL_FLOAT,GL_FALSE,0,0);
    
    glEnableVertexAttribArray(RENDER_UV_LOCATION);
    glBindBuffer(GL_ARRAY_BUFFER,buffers[1]);
    glBufferData(GL_ARRAY_BUFFER,uvCoordinats.size() * sizeof(glm::vec2),&uvCoordinats[0],GL_STATIC_DRAW);
    glVertexAttribPointer(RENDER_UV_LOCATION,2,GL_FLOAT,GL_FALSE,0,0);
    
    
    glDrawArrays(GL_TRIANGLES, 0, (GLint)vertices.size());
    
    glDeleteBuffers(2,buffers);
    glBindTexture(GL_TEXTURE_2D,0);

	return true;
}

And the Shaders for the sake of it:

Vertex:

#version 150
in vec2 in_Position;
in vec2 in_UV;

out vec2 ex_UV;

void main(void)
{
    //Position is in a Range of [0,500]*[0,500] and has to be mapped to [-1,1]*[-1,1]
    vec2 out_Position = in_Position - vec2(250,250);
    out_Position = out_Position / vec2(250,250);
	gl_Position = vec4(out_Position,0,1);
	ex_UV = in_UV;
}

Fragment:

#version 150
in vec2 ex_UV;

out vec4 out_Color;

uniform sampler2D myTextureSampler;

void main(void)
{
	out_Color = texture(myTextureSampler, ex_UV);
}
Edited by ScherzkeCks
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Print the coordinates of the vertices you are putting into the vertex buffer.  Ensure they are neither too small nor too large.

Disable culling.  Disable depth testing.

 

 

L. Spiro

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I did print the coordinates and made all the math on them by hand. and while certainly a little large for text they all are within the window.

Culling and Depth testing also disabled but no difference. 

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First letter:

 

v1: x:125.000000 y:148.000000 

v2: x:137.000000 y:148.000000 

v3: x:125.000000 y:170.000000 

v4: x:137.000000 y:170.000000 

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gl_Position = vec4(out_Position,0,1);
Change to:
gl_Position = vec4(out_Position,10,1);
or:
gl_Position = vec4(out_Position,-10,1);

L. Spiro
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tried both, nothing changed.

 

Could it be some kind of wrong calls to change states? I will post the only other part of code that makes opengl calls after the creation of the window, maybe I am doing something wrong when switching from Model-Drawing to Text-Drawing.

 

This code gets called right before i call the drawText() function (This part works just fine)

void Render::renderObjects()
{

	glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

	glUseProgram(programID);

	//Texture-Sampler Location
	GLuint textureSampler = glGetUniformLocation(programID,"myTextureSampler");

	GLint vpLocation = glGetUniformLocation(programID,"VP");
	glm::mat4 vp = GameManager::getSingleton()->getCamera()->getCameraMatrix();
	glUniformMatrix4fv(vpLocation,1,GL_FALSE,&vp[0][0]);

	GLint modelMatrixLocation = glGetUniformLocation(programID,"model");

	std::vector<RenderObject *> objectsToRender;

	objectsToRender = GameManager::getSingleton()->getROManager()->getObjectsToRender();



	for (int i = 0; i < objectsToRender.size(); ++i)
	{
		RenderObject *currentObject = objectsToRender.at(i);
		GLuint vertexArrayObjectName = currentObject->getVertexArrayName();
		if (vertexArrayObjectName == 0)
		{
			//Create vertexarrayobject and buffers etc.
			GLfloat* vertices = NULL;
			GLfloat* normals = NULL;
			GLuint* indices = NULL;
			GLfloat* uvCoordinates = NULL;
			int verticesCount;
			int indicesCount;
			short textureWidth, textureHeight;
			char* textureData = NULL;
			try {
				currentObject->getData(&vertices, &normals, &indices, &uvCoordinates, &verticesCount, &indicesCount, &textureWidth, &textureHeight, &textureData);
			}
			catch (RenderObjectException* e) {
				printf("%s\n", e->what());
				//TODO: remove from objectHandler and further error-Handling
				continue;
			}

			//Texture
			GLuint textureID;
			glGenTextures(1, &textureID);
			glBindTexture(GL_TEXTURE_2D, textureID);
			//glTexStorage2D(GL_TEXTURE_2D,4, GL_RGB, textureWidth, textureHeight);
			//glTexSubImage2D(GL_TEXTURE_2D,0,0,0,textureWidth,textureHeight,GL_BGR, GL_UNSIGNED_BYTE, textureData);
			glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, textureWidth, textureHeight, 0, GL_BGR, GL_UNSIGNED_BYTE, textureData); // <- tutorial version but mutable

			glGenerateMipmap(GL_TEXTURE_2D);

			glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR_MIPMAP_NEAREST);
			glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_NEAREST);
			//glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT );
			//glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT );

			currentObject->setTextureID(textureID);

			//creating vertexarray
			glGenVertexArrays(1,&vertexArrayObjectName);
			glBindVertexArray(vertexArrayObjectName);

			currentObject->setVertexArrayName(vertexArrayObjectName);

			//create the buffers belonging to this vertexarray
			GLuint vboId;
			glGenBuffers(1,&vboId);
			glBindBuffer(GL_ARRAY_BUFFER,vboId);
			glBufferData(GL_ARRAY_BUFFER,verticesCount * sizeof(GLfloat) * 4,vertices, GL_STATIC_DRAW);
			glVertexAttribPointer(RENDER_POSITION_LOCATION,4,GL_FLOAT,GL_FALSE,0,0);
			glEnableVertexAttribArray(RENDER_POSITION_LOCATION);

			//normalBuffer
			GLuint normalBuffer;
			glGenBuffers(1,&normalBuffer);
			glBindBuffer(GL_ARRAY_BUFFER,normalBuffer);
			glBufferData(GL_ARRAY_BUFFER, verticesCount * 4 * sizeof(GLfloat),normals, GL_STATIC_DRAW);
			glVertexAttribPointer(RENDER_NORMALS_LOCATION,4,GL_FLOAT,GL_FALSE,0,NULL);
			glEnableVertexAttribArray(RENDER_NORMALS_LOCATION);

			//uvCoordinatesBuffer
			GLuint uvCoordinatesID;
			glGenBuffers(1,&uvCoordinatesID);
			glBindBuffer(GL_ARRAY_BUFFER,uvCoordinatesID);
			glBufferData(GL_ARRAY_BUFFER,verticesCount * sizeof(GLfloat) * 2,uvCoordinates,GL_STATIC_DRAW);
			glVertexAttribPointer(RENDER_UV_LOCATION,2,GL_FLOAT,GL_FALSE,0,0);
			glEnableVertexAttribArray(RENDER_UV_LOCATION);

			GLuint indicesID;
			glGenBuffers(1,&indicesID);
			glBindBuffer(GL_ELEMENT_ARRAY_BUFFER,indicesID);
			glBufferData(GL_ELEMENT_ARRAY_BUFFER,indicesCount * sizeof(GLuint),indices,GL_STATIC_DRAW);

			glBindVertexArray(0);


		}


		glActiveTexture(GL_TEXTURE0);
		glBindTexture(GL_TEXTURE_2D, currentObject->getTextureID());
		glUniform1i(textureSampler,0);

		glm::mat4  modelMatrix = currentObject->getModelMatrix();

		glUniformMatrix4fv(modelMatrixLocation,1,GL_FALSE,&modelMatrix[0][0]);

		glBindVertexArray(vertexArrayObjectName);

		glDrawElements(GL_TRIANGLES,currentObject->getIndicesCount(),GL_UNSIGNED_INT,0);

		glBindVertexArray(0);
		

	}
	
}

Edited by ScherzkeCks
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Have you tried replacing the fragment shader by writing out just white, just to make sure that the texture coordinates are not wrong? I would suggest you make the code as minimal as possible, I think that is the best way to find out this kind of bugs. Comment out all unnecessary stuff, render the text and do nothing else and see if that works. 

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Well I am down to just glClear() the TextDrawing code and the buffer swapping. Also the vertex-Shader only outputs white now. Still only a black screen.

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Had to try it myself, the code you have shown seems ok. This draws pink quads for the characters:

// g++ -std=c++11 text.cpp $(pkg-config --libs --cflags sdl glew) && ./a.out
#include <iostream>
#include <vector>

#include "SDL.h"
#include <GL/glew.h>
#include <glm/glm.hpp>

unsigned int program;

const char *vs_source = 
"#version 150\n"
"in vec2 in_Position;\n"
"void main(void) {\n"
"    //Position is in a Range of [0,500]*[0,500] and has to be mapped to [-1,1]*[-1,1]\n"
"    vec2 out_Position = in_Position - vec2(250);\n"
"    out_Position = out_Position / vec2(250);\n"
"    gl_Position = vec4(out_Position,0,1);\n"
"}\n";

const char *fs_source = 
"#version 150\n"
"out vec4 out_Color;\n"
"void main(void) {\n"
"    out_Color = vec4(1,0,1,1);\n"
"}\n";

unsigned int program_create() {
    GLuint p = glCreateProgram();
    GLuint vs = glCreateShader(GL_VERTEX_SHADER);
    GLuint fs = glCreateShader(GL_FRAGMENT_SHADER);

    glShaderSource(vs, 1, &vs_source, 0);
    glAttachShader(p, vs);
    glCompileShader(vs);

    glShaderSource(fs, 1, &fs_source, 0);
    glCompileShader(fs);
    glAttachShader(p, fs);

    glBindAttribLocation(p, 0, "in_Position");

    glLinkProgram(p);

    return p;
}

bool drawText(int x, int y, const std::string &text) {
    std::vector<glm::vec2> vertices;

    float offsetx = x;
    float offsety = y;
    for(size_t i=0; i<text.size(); ++i) {
        glm::vec2 v1 = glm::vec2(offsetx, offsety);
        glm::vec2 v2 = glm::vec2(offsetx+10, offsety);
        glm::vec2 v3 = glm::vec2(offsetx, offsety+20);
        glm::vec2 v4 = glm::vec2(offsetx+10, offsety+20);
        vertices.push_back(v1);
        vertices.push_back(v2);
        vertices.push_back(v3);
        vertices.push_back(v3);
        vertices.push_back(v2);
        vertices.push_back(v4);
       offsetx += 15;
    }

    glUseProgram(program);

    GLuint vbo;
    glGenBuffers(1, &vbo);

    glEnableVertexAttribArray(0);
    glBindBuffer(GL_ARRAY_BUFFER, vbo);
    glBufferData(GL_ARRAY_BUFFER, vertices.size() * sizeof(glm::vec2), &vertices[0], GL_STATIC_DRAW);
    glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE,0,0);

    glDrawArrays(GL_TRIANGLES, 0, (GLint)vertices.size());

    glDeleteBuffers(1, &vbo);
    glBindTexture(GL_TEXTURE_2D,0);

    return true;
}

int main(int argc, char **argv) {
    bool running = true;

    SDL_Init(SDL_INIT_EVERYTHING);
    SDL_SetVideoMode(1280, 800, 0, SDL_OPENGL);

    glewInit();

    program = program_create();

    SDL_Event event;
    while(running) {
        while(SDL_PollEvent(&event)) {
            switch(event.type) {
                case SDL_QUIT: running = false; break;
                case SDL_KEYDOWN: running = !(event.key.keysym.sym == SDLK_ESCAPE); break;
            }
        }
        glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
        drawText(250, 250, "hello");
        SDL_GL_SwapBuffers();
        assert(glGetError() == GL_NO_ERROR);
    }

    SDL_Quit();
    return 0;
}
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Yeah, but then it has to be something in between that code and the objectdrawing code which works too.

 

But I am not doing anything in between other than what is written in the code above. The drawText method gets called literally right after the renderObjects() call. 

But even if I just call the drawText() code it doesn't work

 

Just for your information, I am using GLFW instead of SDL but that shouldn't matter as far as I can tell. 

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Alright, I solved it. And because somebody might search this in the future I will post the solution here:

 

I had to use a VertexArrayObject for the text, then it would draw just fine.

 

I was under the impression, that you don't have to use VAOs but I guess I was wrong.

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I believe VAO was made mandatory in OpenGL 4.0 or thereabout. In any case, yes, it is mandatory to use VAO in later versions at least.

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