First im rendering a triangle to a texture then rendering the texture to the screen with a blurry shader effect. It works as expected as long as im just rendering the triangle to the texture once before the main loop. But as soon as I continuously render the triangle in the main loop to the texture, the texture seems to be empty and the triangle is no longer visible. Why does the rendering to texture stops working once it is continuously executed in the main loop?
Below is the corresponding code. The code is divided in four steps. First the framebuffer and the texture is created(1), then the VAO and program for the rendering of the triangle is created(2). After the triangle is rendered to the texture(3) the texture is rendered on a quad to the screen(4). The problem occurs as soon as Step 4 is executed together with Step 3 in the main loop, the texture appears empty and no triangle is visible.
- Create Framebuffer and Texture
- Create VAO and program for Triangle
- Render Triangle to Texture
- Render Quad with Texture to Screen (Inside main loop)
//===> STEP 1: Create Framebuffer and Texture
// The framebuffer, which regroups 0, 1, or more textures, and 0 or 1 depth buffer.
GLuint FramebufferName = 0;
glGenFramebuffers(1, &FramebufferName);
glBindFramebuffer(GL_FRAMEBUFFER, FramebufferName);
// The texture we're going to render to
GLuint renderedTexture;
glGenTextures(1, &renderedTexture);
// "Bind" the newly created texture : all future texture functions will modify this texture
glBindTexture(GL_TEXTURE_2D, renderedTexture);
// Give an empty image to OpenGL ( the last "0" means "empty" )
glTexImage2D(GL_TEXTURE_2D, 0,GL_RGB, windowWidth, windowHeight, 0,GL_RGB, GL_UNSIGNED_BYTE, 0);
// Poor filtering
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
// The depth buffer
GLuint depthrenderbuffer;
glGenRenderbuffers(1, &depthrenderbuffer);
glBindRenderbuffer(GL_RENDERBUFFER, depthrenderbuffer);
glRenderbufferStorage(GL_RENDERBUFFER, GL_DEPTH_COMPONENT, windowWidth, windowHeight);
glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_RENDERBUFFER, depthrenderbuffer);
// Set "renderedTexture" as our colour attachement #0
glFramebufferTexture(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, renderedTexture, 0);
// Set the list of draw buffers.
GLenum DrawBuffers[1] = {GL_COLOR_ATTACHMENT0};
glDrawBuffers(1, DrawBuffers); // "1" is the size of DrawBuffers
// Always check that our framebuffer is ok
if(glCheckFramebufferStatus(GL_FRAMEBUFFER) != GL_FRAMEBUFFER_COMPLETE)
return false;
//<=== Create Framebuffer and Texture
//==> STEP 2: Create VAO and program for Triangle
static Vert vertices[3] =
{
{ { -.1f, -0.1f }, { 1.f, 0.f, 0.f } },
{ { 0.1f, -0.1f }, { 0.f, 1.f, 0.f } },
{ { 0.f, 0.1f }, { 0.f, 0.f, 1.f } }
};
GLuint vertex_buffer;
glGenBuffers(1, &vertex_buffer);
glBindBuffer(GL_ARRAY_BUFFER, vertex_buffer);
glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), &vertices, GL_DYNAMIC_DRAW);
const GLuint vertex_shader = glCreateShader(GL_VERTEX_SHADER);
glShaderSource(vertex_shader, 1, &vertex_shader_source, NULL);
glCompileShader(vertex_shader);
const GLuint fragment_shader = glCreateShader(GL_FRAGMENT_SHADER);
glShaderSource(fragment_shader, 1, &fragment_shader_source, NULL);
glCompileShader(fragment_shader);
const GLuint program = glCreateProgram();
glAttachShader(program, vertex_shader);
glAttachShader(program, fragment_shader);
glLinkProgram(program);
const GLint mvp_location = glGetUniformLocation(program, "MVP");
const GLint vpos_location = glGetAttribLocation(program, "vPos");
const GLint vcol_location = glGetAttribLocation(program, "vCol");
GLuint vertex_array;
glGenVertexArrays(1, &vertex_array);
glBindVertexArray(vertex_array);
glEnableVertexAttribArray(vpos_location);
glVertexAttribPointer(vpos_location, 2, GL_FLOAT, GL_FALSE,
sizeof(Vert), (void*) offsetof(Vert, pos));
glEnableVertexAttribArray(vcol_location);
glVertexAttribPointer(vcol_location, 3, GL_FLOAT, GL_FALSE,
sizeof(Vert), (void*) offsetof(Vert, col));
//<== Create VAO and program for Triangle
//==> Create VBO and program for Quad
static const GLfloat g_quad_vertex_buffer_data[] = {
-1.0f, -1.0f, 0.0f,
1.0f, -1.0f, 0.0f,
-1.0f, 1.0f, 0.0f,
-1.0f, 1.0f, 0.0f,
1.0f, -1.0f, 0.0f,
1.0f, 1.0f, 0.0f,
};
GLuint quad_vertexbuffer;
glGenBuffers(1, &quad_vertexbuffer);
glBindBuffer(GL_ARRAY_BUFFER, quad_vertexbuffer);
glBufferData(GL_ARRAY_BUFFER, sizeof(g_quad_vertex_buffer_data), g_quad_vertex_buffer_data, GL_STATIC_DRAW);
const GLuint vertex_shader2 = glCreateShader(GL_VERTEX_SHADER);
glShaderSource(vertex_shader2, 1, &vertex_shader_source2, NULL);
glCompileShader(vertex_shader2);
const GLuint fragment_shader2 = glCreateShader(GL_FRAGMENT_SHADER);
glShaderSource(fragment_shader2, 1, &fragment_shader_source2, NULL);
glCompileShader(fragment_shader2);
const GLuint quad_programID = glCreateProgram();
glAttachShader(quad_programID, vertex_shader2);
glAttachShader(quad_programID, fragment_shader2);
glLinkProgram(quad_programID);
GLuint texID = glGetUniformLocation(quad_programID, "renderedTexture");
GLuint timeID = glGetUniformLocation(quad_programID, "time");
//<== Create VBO and program for Quad
//===> STEP 3: Render Triangle to Texture
glBindFramebuffer(GL_FRAMEBUFFER, FramebufferName);
glViewport(0,0,windowWidth,windowHeight); // Render on the whole framebuffer, complete from the lower left corner to the upper right
// Clear the screen
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glUseProgram(program);
// Bind our texture in Texture Unit 0
glActiveTexture(GL_TEXTURE0);
glBindVertexArray(vertex_array);
glDrawArrays(GL_TRIANGLES, 0, 3);
//<=== Render Triangle to Texture
do{
// !!! No Triangle visible if "STEP 3: Render Triangle to Texture" here
//==> STEP 4: Render Quad with Texture to Screen
// Render to the screen
glBindFramebuffer(GL_FRAMEBUFFER, 0);
// Render on the whole framebuffer, complete from the lower left corner to the upper right
glViewport(0,0,windowWidth,windowHeight);
// Clear the screen
glClear( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
// Use our shader
glUseProgram(quad_programID);
// Bind our texture in Texture Unit 0
glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_2D, renderedTexture);
// Set our "renderedTexture" sampler to use Texture Unit 0
glUniform1i(texID, 0);
glUniform1f(timeID, (float)(glfwGetTime()*10.0f) );
// 1rst attribute buffer : vertices
glEnableVertexAttribArray(0);
glBindBuffer(GL_ARRAY_BUFFER, quad_vertexbuffer);
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, (void*)0);
// Draw the Quad
glDrawArrays(GL_TRIANGLES, 0, 6); // 2*3 indices starting at 0 -> 2 triangles
glDisableVertexAttribArray(0);
//<== Render Quad with Texture to Screen
// Swap buffers
glfwSwapBuffers(window);
glfwPollEvents();
} // Check if the ESC key was pressed or the window was closed
while( glfwGetKey(window, GLFW_KEY_ESCAPE ) != GLFW_PRESS &&
glfwWindowShouldClose(window) == 0 );
I have just started with OpenGL and even after a lot of back and forth I can’t get any further here. Thanks in advance for any help.