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SDL2 iOS OpenGL es 3.0 simple triangle example not working
josh43


Joined: 14 Aug 2015
Posts: 4
Post Posted: Mon Aug 17, 2015 1:08 am
Hello guys, could anyone tell me why this simple example will not display anything?

Main
Code:

//
//  main.cpp
//  ___PROJECTNAME___
//
//  Created on 8/14/15.
//
//
#include <OpenGLES/ES3/gl.h>
#include <OpenGLES/ES3/glext.h>
#include "SDL.h"

#include "Shader.h"

#define TRIANGLE_DEMO
static const GLfloat cube_vertices[] = {
    // front
    -1.0, -1.0,  1.0,
    1.0, -1.0,  1.0,
    1.0,  1.0,  1.0,
    -1.0,  1.0,  1.0,
    // back
    -1.0, -1.0, -1.0,
    1.0, -1.0, -1.0,
    1.0,  1.0, -1.0,
    -1.0,  1.0, -1.0,
};
static const GLushort cube_elements[] = {
    // front
    0, 1, 2,
    2, 3, 0,
    // top
    3, 2, 6,
    6, 7, 3,
    // back
    7, 6, 5,
    5, 4, 7,
    // bottom
    4, 5, 1,
    1, 0, 4,
    // left
    4, 0, 3,
    3, 7, 4,
    // right
    1, 5, 6,
    6, 2, 1,
};
static const GLfloat triangle[] = {
    -1.0f, 0.0f, 0.0f,
    0.0f, 1.0f, 0.0f,
    0.0f,  1.0f, 0.0f,
};
void update(void * window){
   
}
void cubeDrawer(SDL_Window * window){
    SDL_Window * win = ((SDL_Window *)window);
    glClearColor(1.0f, 0.0f, 0.0f, 1.0f);
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
   
    SDL_GL_SwapWindow(win);
}
void triangleDrawer(SDL_Window  * window){
     Shader tShader("triangleShader");
    GLuint vao, vbo;
   
    glGenVertexArrays(1, &vao);
    glBindVertexArray(vao);
   
    glGenBuffers(1, &vbo);
    glBindBuffer(GL_ARRAY_BUFFER, vbo);
    glBufferData(GL_ARRAY_BUFFER, sizeof(triangle),triangle,GL_STATIC_DRAW);
   
    glEnableVertexAttribArray(0);
    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, 0);
   
   
    //SDL_iPhoneSetAnimationCallback(window, 10, update, nullptr);
    while(true){
        glClearColor(1.0f, 0.0f, 0.0f, 1.0f);
        glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
       
        // Oddly enough If I do not include these next 2 lines
        // it will not even clear the color of the backscreen!
        SDL_Event e;
        SDL_PollEvent(&e);
       
       
        tShader.bind(); // glUseProgram(my_shader_id);
        glBindVertexArray(vao);
        glDrawArrays(GL_TRIANGLES, 0, 3);
       
       
        SDL_GL_SwapWindow(window);
    }
   
}
int
main(int argc, char *argv[])
{
   
    SDL_Window *window = nullptr;
   
    if (SDL_Init(SDL_INIT_VIDEO) !=0) {
        printf("Could not initialize SDL\n");
        return 1;
    }
    if(SDL_GL_SetAttribute(SDL_GL_CONTEXT_PROFILE_MASK, SDL_GL_CONTEXT_PROFILE_ES)!=0){
        std::cout << "ERROR loading context profile mask\n";
    }
    if(SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 3)!=0){
        std::cout <<"ERROR setting context major version\n";
    }
    if(SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 0)!=0){
        std::cout <<"ERROR setting context minor version\n";
    }
    if(SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER, 1) != 0){
        std::cout << " ERrror \n setting double buffer";
    } // I have tried without the dubble buffer and nothing changes
    if(SDL_GL_SetAttribute(SDL_GL_DEPTH_SIZE   , 24) != 0){
        std::cout << " ERrror \n setting depth buffer";
    }
   
   
   
    SDL_DisplayMode display;
    SDL_GetDesktopDisplayMode(0, &display);
   
 
    window = SDL_CreateWindow(NULL, 0, 0, display.w, display.h, SDL_WINDOW_OPENGL | SDL_WINDOW_FULLSCREEN);
    assert(window != nullptr);
   
    SDL_GLContext  glContext = SDL_GL_CreateContext(window);
    assert(glContext != NULL);
   
   
#ifdef TRIANGLE_DEMO
    triangleDrawer(window);
#else
    cubeDrawer(window);
   
#endif

    return 1;
}


Shader


Code:
#include "Shader.h"

static std::string LoadShader(const std::string &fileName);


Shader::Shader(const std::string & fileName)
{
   m_program = glCreateProgram();
   m_shaders[0] = CreateShader(LoadShader(fileName + ".vs"), GL_VERTEX_SHADER);
   m_shaders[1] = CreateShader(LoadShader(fileName + ".fs"), GL_FRAGMENT_SHADER);

   for (int i = 0; i < NUM_SHADERS; i++) {
      glAttachShader(m_program, m_shaders[i]);

   }

   glBindAttribLocation(m_program, 0, "position");
   //glBindAttribLocation(m_program, 1, "normal");
   //glBindAttribLocation(m_program, 2, "textureCoord");

   glLinkProgram(m_program);
   CheckShaderError(m_program, GL_LINK_STATUS, true, "Error linking shader program");

   glValidateProgram(m_program);
   CheckShaderError(m_program, GL_LINK_STATUS, true, "Invalid shader program");


   
   /*
   uniform mat4 model;
   uniform mat4 viewProjection;

   */
   

}

void Shader::CheckShaderError(GLuint shader, GLuint flag, bool isProgram, const std::string& errorMessage)
{
   GLint success = 0;
   GLchar error[1024] = { 0 };

   if (isProgram)
      glGetProgramiv(shader, flag, &success);
   else
      glGetShaderiv(shader, flag, &success);

   if (success == GL_FALSE)
   {
      if (isProgram)
         glGetProgramInfoLog(shader, sizeof(error), NULL, error);
      else
         glGetShaderInfoLog(shader, sizeof(error), NULL, error);

      std::cerr << errorMessage << ": '" << error << "'" << std::endl;
   }
}
void Shader::updateShadowMatrix(glm::mat4 &shadowM)
{
   glUniform4fv(m_uniforms[SHADOW_MATRIX], 1, &shadowM[0][0]);
}
 GLuint Shader::CreateShader(const std::string &fullText, GLenum typeShader) {
   GLuint shader = glCreateShader(typeShader);

   const GLchar * shaderSourceString[1];
   GLint shaderSourceStringLength[1];

   shaderSourceString[0] = fullText.c_str();
   shaderSourceStringLength[0] = (GLint)fullText.length();
   glShaderSource(shader, 1, shaderSourceString, shaderSourceStringLength);
   glCompileShader(shader);

   CheckShaderError(shader, GL_COMPILE_STATUS, false, "Error compiling shader!");

   
   return shader;


}

static std::string LoadShader(const std::string &fileName) {
   std::ifstream file;
   file.open(fileName.c_str());

   std::string output;
   std::string line;
   if (file.is_open()) {
      while (file.good()) {
         getline(file, line);
         output.append(line + '\n');
      }
   }
   else {
      std::cerr << "ERror reading the file ";
   }

   return output;
}
void Shader::bind()
{
   glUseProgram(m_program);
}

/*void Shader::update(Transform& trans, const Camera & cam)
{
   glm::mat4 view = cam.getCameraMatrix();
   glm::mat4 viewP = cam.getViewProjection();
   glm::mat4 model = trans.getModelMatrix();
   view = view * model;
   glUniformMatrix4fv(m_uniforms[MODEL_U], 1, GL_FALSE, &model[0][0]);
   glUniformMatrix4fv(m_uniforms[VIEWPROJECTION_U], 1, GL_FALSE, &viewP[0][0]);
   glUniformMatrix4fv(m_uniforms[MODEL_VIEW], 1, GL_FALSE, &view[0][0]);

}
*/

Shader::~Shader()
{
   for (int i = 0; i < NUM_SHADERS; i++) {
      glDetachShader(m_program, m_shaders[i]);
      glDeleteShader(m_shaders[i]);
   }
   glDeleteProgram(m_program);
}


//triangleShader.vs
Code:
 
#version 300 es
layout(location = 0) in highp vec3 position;

out highp vec3 colorPosition;
void main(){
    colorPosition = position;
    gl_Position = vec4(position,1.0f);
}


Code:

#version 300 es


in highp vec3 colorPosition;
out highp vec4 color;
void main(){
    color = vec4(colorPosition,1.0f);
}
josh43


Joined: 14 Aug 2015
Posts: 4
Post Posted: Tue Aug 18, 2015 5:20 am
I needed to set glViewPort(.....)