render image to fullscreen quad

res/container.jpg

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:126baccff187648acfad78c57560035f5c783cc6ec92a37a93a5b1edc97af10e
+size 184939

res/shader/shader.frag

@@ -2,8 +2,11 @@
 out vec4 FragColor;
 
 in vec3 ourColor;
+in vec2 TexCoord;
+
+uniform sampler2D ourTexture;
 
 void main()
 {
-    FragColor = vec4(ourColor, 1.0);
+    FragColor = texture(ourTexture, TexCoord);
 }

res/shader/shader.vert

@@ -1,11 +1,14 @@
 #version 330 core
 layout (location = 0) in vec3 aPos;         // position has attribute position 0
 layout (location = 1) in vec3 aColor;       // color has attribute position 1
+layout (location = 2) in vec2 aTexCoord;    // texture coordinate
 
 out vec3 ourColor;
+out vec2 TexCoord;
 
 void main()
 {
     gl_Position = vec4(aPos, 1.0);
     ourColor = aColor;
+    TexCoord = aTexCoord;
 }

src/main.c

@@ -1,13 +1,14 @@
 #include "main.h"
 
 #include "gfx.h"
+#include "stb_image.h"
 
 float vertices[] = {
-    // position             color
-     0.5f,  0.5f,  0.0f,    1.0f, 1.0f, 1.0f,  // top right
-     0.5f, -0.5f,  0.0f,    1.0f, 0.0f, 0.0f,  // bottom right
-    -0.5f, -0.5f,  0.0f,    0.0f, 1.0f, 0.0f,  // bottom left
-    -0.5f,  0.5f,  0.0f,    0.0f, 0.0f, 1.0f   // top left
+    // position             color               uvs
+     1.0f,  1.0f,  0.0f,    1.0f, 0.0f, 0.0f,   1.0f, 1.0f, // top right
+     1.0f, -1.0f,  0.0f,    0.0f, 1.0f, 0.0f,   1.0f, 0.0f, // bottom right
+    -1.0f, -1.0f,  0.0f,    0.0f, 0.0f, 1.0f,   0.0f, 0.0f, // bottom left
+    -1.0f,  1.0f,  0.0f,    1.0f, 1.0f, 0.0f,   0.0f, 1.0f  // top left
 };
 
 unsigned int indices[] = {
@@ -28,6 +29,33 @@ int main()
     gfxInit();
     SDL_Window* window = getWindow();
 
+    // generate opengl texture
+    unsigned int texture;
+    glGenTextures(1, &texture);
+    glBindTexture(GL_TEXTURE_2D, texture);
+    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
+    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
+    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
+    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
+
+    // load image data from file
+    const char* imageFile = "res/tex.png";
+    int width, height, nrChannels;
+    stbi_set_flip_vertically_on_load(1);
+    unsigned char* data = stbi_load(imageFile, &width, &height, &nrChannels, 0);
+    if (!data)
+    {
+        fputs("failed to load texture data: ", stderr);
+        fputs(imageFile, stderr);
+        fputs("\n", stderr);
+        exit(1);
+    }
+    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, data);
+    glGenerateMipmap(GL_TEXTURE_2D);
+
+    // free loaded image data
+    stbi_image_free(data);
+
     unsigned int shaderProgram = compileShaderProgram();
 
     // vertex array object
@@ -52,12 +80,16 @@ int main()
 
     // set vertex attributes
 
+    int stride = 8*sizeof(float);
     // position attribute
-    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 6*sizeof(float), (void*)0); // TODO: wtf
+    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, stride, (void*)0); // TODO: wtf
     glEnableVertexAttribArray(0);
     // color attribute
-    glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, 6*sizeof(float), (void*)(3 * sizeof(float)));
+    glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, stride, (void*)(3 * sizeof(float)));
     glEnableVertexAttribArray(1);
+    // uv attribute
+    glVertexAttribPointer(2, 2, GL_FLOAT, GL_FALSE, stride, (void*)(6 * sizeof(float)));
+    glEnableVertexAttribArray(2);
 
     glUseProgram(shaderProgram);
 
@@ -69,10 +101,10 @@ int main()
         glClear(GL_COLOR_BUFFER_BIT);
 
         // update uniforms
-        float time = (float)SDL_GetTicks() / 1000.0f;
-        float greenValue = (sin(time)/2.0f)+0.5f;
-        int vertexColorLocation = glGetUniformLocation(shaderProgram, "ourColor");
-        glUniform4f(vertexColorLocation, 0.0f, greenValue, 0.0f, 1.0f);
+        //float time = (float)SDL_GetTicks() / 1000.0f;
+        //float greenValue = (sin(time)/2.0f)+0.5f;
+        //int vertexColorLocation = glGetUniformLocation(shaderProgram, "ourColor");
+        //glUniform4f(vertexColorLocation, 0.0f, greenValue, 0.0f, 1.0f);
 
         // draw
         glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, 0);

src/stb_image.c

@@ -0,0 +1,2 @@
+#define STB_IMAGE_IMPLEMENTATION
+#include "stb_image.h"

todo.md

@@ -1,4 +1,4 @@
 * [x] basic opengl initialisation
-* [ ] render a texture to a full-screen quad
+* [x] render a texture to a full-screen quad
 * [ ] output image to a file
 * [ ] render image with compute shader