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OpenGL How to render multiple objects with different shaders

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I'm looking to render multiple objects (rectangles) with different shaders. So far I've managed to render one rectangle made out of 2 triangles and apply shader to it, but when it comes to render another I get stucked. Searched for documentations or stuffs that could help me, but everything shows how to render only 1 object. Any tips or help is highly appreciated, thanks!

Here's my code for rendering one object with shader!

 

	#define GLEW_STATIC
	
	#include <stdio.h>
	#include <GL/glew.h>
	#include <GLFW/glfw3.h>
	
	#include "window.h"
	
	#define GLSL(src) "#version 330 core\n" #src
	// #define ASSERT(expression, msg) if(expression) {fprintf(stderr, "Error on line %d: %s\n", __LINE__, msg);return -1;}
	
	int main() {
	    // Init GLFW
	    if (glfwInit() != GL_TRUE) {
	        std::cerr << "Failed to initialize GLFW\n" << std::endl;
	        exit(EXIT_FAILURE);
	    }
	    // Create a rendering window with OpenGL 3.2 context
	    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
	    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 2);
	    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
	    glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE);
	    glfwWindowHint(GLFW_RESIZABLE, GL_FALSE);
	
	    // assing window pointer
	    GLFWwindow *window = glfwCreateWindow(800, 600, "OpenGL", NULL, NULL);
	    glfwMakeContextCurrent(window);
	    // Init GLEW
	    glewExperimental = GL_TRUE;
	    if (glewInit() != GLEW_OK) {
	        std::cerr << "Failed to initialize GLEW\n" << std::endl;
	        exit(EXIT_FAILURE);
	    }
	    // ----------------------------- RESOURCES ----------------------------- //
	
	    // create gl data
	    const GLfloat positions[8] = {
	        -0.5f, -0.5f,
	         0.5f, -0.5f,
	         0.5f,  0.5f,
	        -0.5f, 0.5f,
	    };
	
	    const GLuint elements[6] = {
	        0, 1, 2,
	        2, 3, 0
	    };
	
	    // Create Vertex Array Object
	    GLuint vao;
	    glGenVertexArrays(1, &vao);
	    glBindVertexArray(vao);
	
	    // Create a Vertex Buffer Object and copy the vertex data to it
	    GLuint vbo;
	    glGenBuffers(1, &vbo);
	    glBindBuffer(GL_ARRAY_BUFFER, vbo);
	    glBufferData(GL_ARRAY_BUFFER, sizeof(positions), positions, GL_STATIC_DRAW);
	    // Specify the layout of the vertex data
	    glEnableVertexAttribArray(0); // layout(location = 0)
	    glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE, 0, 0);
	    
	    // Create a Elements Buffer Object and copy the elements data to it
	    GLuint ebo;
	    glGenBuffers(1, &ebo);
	    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, ebo);
	    glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(elements),  elements, GL_STATIC_DRAW);
	    
	
	    // Create and compile the vertex shader
	    const GLchar *vertexSource = GLSL(
	        layout(location = 0) in vec2 position;
	        
	        void main() {
	            gl_Position = vec4(position, 0.0, 1.0);
	        }
	    );
	
	    GLuint vertexShader = glCreateShader(GL_VERTEX_SHADER);
	    glShaderSource(vertexShader, 1, &vertexSource, NULL);
	    glCompileShader(vertexShader);
	
	    // Create and compile the fragment shader
	    const char* fragmentSource = GLSL(
	        out vec4 gl_FragColor;
	        uniform vec2 u_resolution;
	        
	        void main() {
	            vec2 pos = gl_FragCoord.xy / u_resolution;
	          
	            gl_FragColor = vec4(1.0);
	        }
	    );
	
	    GLuint fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);
	    glShaderSource(fragmentShader, 1, &fragmentSource, NULL);
	    glCompileShader(fragmentShader);
	
	    // Link the vertex and fragment shader into a shader program
	    GLuint shaderProgram = glCreateProgram();
	    glAttachShader(shaderProgram, vertexShader);
	    glAttachShader(shaderProgram, fragmentShader);
	    glLinkProgram(shaderProgram);
	    glUseProgram(shaderProgram);
	
	    // get uniform's id by name and set value
	    GLint uRes = glGetUniformLocation(shaderProgram, "u_Resolution");
	    glUniform2f(uRes, 800.0f, 600.0f);
	        
	    // ---------------------------- RENDERING ------------------------------ //
	
	    while(!glfwWindowShouldClose(window)) {
	        // Clear the screen to black
	        glClear(GL_COLOR_BUFFER_BIT);
	        glClearColor(0.0f, 0.5f, 1.0f, 1.0f);
	        
	        // Draw a rectangle made of 2 triangles -> 6 vertices
	        glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, NULL);
	
	        // Swap buffers and poll window events
	        glfwSwapBuffers(window);
	        glfwPollEvents();
	    }
	
	    // ---------------------------- CLEARING ------------------------------ //
	
	    // Delete allocated resources
	    glDeleteProgram(shaderProgram);
	    glDeleteShader(fragmentShader);
	    glDeleteShader(vertexShader);
	    glDeleteBuffers(1, &vbo);
	    glDeleteVertexArrays(1, &vao);
	
	    return 0;
	}

 

Edited by alex1997

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Without seeing how you are currently doing it, I can only really give a generic example, but you basically just want to create all your shaders, select the shader you wish to use - render all items that use this shader, switch to the next shader, render all items that use that shader, and so on

Switching shaders can be expensive, so thats why you will want to do all items for each shader before moving to the next, rather then switching shaders depending on what your rendering at the time.

If you can show a small bit of code of how you are currently doing this, im sure you will get more specific anwers

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26 minutes ago, McGrane said:

Without seeing how you are currently doing it, I can only really give a generic example, but you basically just want to create all your shaders, select the shader you wish to use - render all items that use this shader, switch to the next shader, render all items that use that shader, and so on

Switching shaders can be expensive, so thats why you will want to do all items for each shader before moving to the next, rather then switching shaders depending on what your rendering at the time.

If you can show a small bit of code of how you are currently doing this, im sure you will get more specific anwers

Thanks! I've pasted my code above And yes, beofre rendering wanna attach the shader and when the objects are ready draw them.

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Yeah, so in the above, you are creating a shader- and then telling opengl to use this shader:

glUseProgram(shaderProgram);

If you wish to use another shader, you do the same as you have done above in creating, compiling and linking another shader. You may want to extend your above to read shaders from text files instead of implementing them in code, and maybe making a shader class to encapsulate all these methods to just make it easier for maintainability. However to just get this working as is, say you have two shaders, and have compiled the into shaderProgram1 and shaderProgram2 then too use them you could just do something like:

3 hours ago, alex1997 said:

glUseProgram(shaderProgram1);

// Draw a rectangle made of 2 triangles -> 6 vertices glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, NULL);

glUseProgram(shaderProgram2);

// Draw a rectangle made of 2 triangles -> 6 vertices glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, NULL);

If you haven't already, check out https://learnopengl.com/ there are sections on shaders, and code examples for how he has set up his shader classes - along with alot of other great information

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      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.
    • By Snaked
      Im working in this project for 1 year .... mostly i develop a tool and databases for make the different maps and now i'm doing the client for play the game
      Tell me if you like it......
      this is a capture of how is viewing atm

       
       
      https://youtu.be/9251v4wDTQ0
    • By RoKabium Games
      Another one of our new UI for #screenshotsaturday. This is the inventory screen for showing what animal fossils you have collected so far. #gamedev #indiedev #sama
    • By Dave Haylett
      Hi everyone. I need some help with my project. It's a 2D-graphics-heavy WPF front-end app written in C#, which talks to two Access 2000 databases (yes I know, it's all I've got). It will be distributed freely on the internet, and so will be being used by Windows users of various installations/versions of Windows, Office, etc.
      One of the two databases (let's call it A), is intended to be read-only, and will be distributed with the app. It has half a dozen relational tables which I as the developer have populated, and is connected to in the app via OleDB Jet 4 with SQL querying the data now and then as the user uses the front-end. The database will be replaced whenever I release an update to the app.
      Database B is read/write, and contains end-user preferences, for example when they favourite something in my front-end, a Favourites table in here gets appended to. This database is not distributed with my app, and should not be overwritten, as it will lose user prefs, etc. and annoy my users.
      Whenever my app is run by a user, during initialisation database A will suck in the user data from database B (using simple SQL SELECT * INTO...), so that all the tables can be joined together by the SQL in database A (to include user prefs/favourites in SQL queries), and whenever the user favourites something, a record is created both in A (for the short-term session) and B (permanently). Database B isn't just about holding favourites, there is other user data in here as well, so there are 3 or 4 tables in B.
      So far, this is all working fine and I'm happy...
      Unfortunately my app is currently 32-bit, and it now needs to break the 32-bit memory barrier what with the size and volume of the graphics I'm pulling in (using the HDD is not really an option, as different graphics are needed kind of instantly and the hard disc would be being hosed and the app dog-slow otherwise, I suspect even off an SSD).
      I'm using VS2015, and switching to 64-bit will probably fix the memory problem, but it breaks Jet 4.0. I'm sure this is old news to most of you.
      To try to keep with 32-bit (and Jet4) but get the memory I need I've tried the -largeaddressaware toggle, and I've tried the editbin suggestion, but I just can't get these solutions to work in VS2015 no matter how hard I try. Are these definitely 100% solutions to 2gb memory limit in 32-bit applications? Should they always work? Am I dumb in being unable to get this to work?
      So otherwise I'm resigned to migrating to 64-bit, and having to get around the database issue, not the memory issue.
      My users will be using a variety of Windows versions (probably 7 and 10), and I'm sure various versions of Office, and so my solution for querying my two Access databases needs to be pretty open if possible.
      Googling has suggested I switch from JET4 to ACE12, but this is apparently requiring me to uninstall Office 2000 and install a 64-bit version (which I don't have), so I can't use it, and I suspect any users who also have an old version of Office installed won't be able to use it either?
      Googling has also suggested I use MS SQL Server. This sounds fine if there's such a thing as a "lite" local version which can manage database access, but I still need to somehow get the data from the databases (A.mdb and B.mdb) into the SQL Server each time the users fire up my app.
      The only solution I can think of at the minute, is to export all the tables from database A into CSVs every time I update the data in there, and have the app import them in a lame way, and also convert database B into some crappy text file which gets written to whenever the user changes a preference. I'd much rather use SQL to do all this if possible, as when the user browses around the app, queries involving joining several tables in A are regularly created and executed to adjust the user's experience/return search results/etc.
      So to summarise my misery, is there either an easy reliable way for me to keep with 32-bit/Jet4 and be able to address >2gb. Or is there instead an easy reliable way for me to switch to 64-bit and successfully query two Access databases without requiring all my users to have 64-bit Office installed?
      Thanks for reading and I hope someone can help.
    • By Alexander Winter
       
        Jumpaï is a game about creating platformer levels and playing them online with everyone. Will you become the most popular level maker or will you be a speedrunner holding world records on everyone's levels? More into casual play? No problems! You can happily play through the giant level database or chill at people's hub. Meet new people, make new friends, learn to master the game by asking pros or ask for people's favorite tricks on level making.  





      Unlike other games of its genre, Jumpaï is about playing levels with everyone in real time. You have the fun to see how other people are playing and get to realize you are not the only one failing that jump!

      The game is currently into development and still have lots to do. I am looking for people willing to help how they can. Developer? Graphist? Play tester? Sound designer? Game designer? I'm welcoming everyone. The project is so big I have a lot of work to do in all areas. Server backend, UI/UX, Game networking, Gameplay and even the website some day. As you can see from the default buttons, the game has been made with LibGDX. 

      If you plan to take an important role into the development of the game, we will discuss how you will get paid once the game generates money. Note that I'm not working on the game full-time. I'm studying full-time and working on it is a hobby. It's been 14 months since it started.

      So, are you interested? If so join me on my discord https://discord.gg/dwRTNCG and I'll answer all your questions.

      Additionnal screenshots:
       



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